PROCESS FOR REMOVING HEAVY METALS FROM SOILS

Abstract: Heavy metals are efficiently removed from contaminated soil by a process which comprises leaching or washing the soil with a mild leachant solution comprised of an aqueous solution of an acid and a salt. Heavy metals are also efficiently removed from paint chips by washing with an aqueous acid. The heavy metals are recovered from the leachant by cementation.

Description: PROCESS FOR REMOVING HEAVY METALS FROM SOIL CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of application serial number 07/771,286, filed on October 3, 1991, the entire contents of which are incorporated herein by reference. BACKGROUND OF THE INVENTION 1. Field of the Invention The invention pertains to a process for removing heavy metals from soil and paint chips. 2. Description of the Related Art The removal of heavy metal contaminants from soils represents a major contemporary environmental problem. Heavy metal pollution can leave the affected ground unusable for agricultural or residential purposes, and the metals can eventually leach into the groundwater system and lead to more widespread problems. While a number of soil classification or solidification/stabilization techniques which leave the offending metals in the soil have been developed, only removal of the metals a'ctually solves the problem "by removing the cause. Several attempts to remove metals from soils have been reported but none have ' been completely successful. One such method is described in Draft Report to the EPA, Contract No. 68-03-3255, US EPA, Emergency Response Branch, Edison , NJ, 1986 and CSIRO Aust. Div. Soils Tech. Pap. No. 41, 1979, 1-17 wherein th extracted metals which were bound to clay .and humi materials were removed with a strong complexing agent suc as EDTA. However, the EDTA remained in the wetted soi causing the treated soil to fail the TCLP test of the EP for extractable metals. Sci. Total Environ. 1989, 7_9_, 253 1 270; Geoderma 1971, 5., 197-208; Soil Sci. Soc. Am. J. 1986, 50 / 598-601; Can. J. Soil Sci. 1976, 56, 37-42; Can. J. Soil Sci. 1969, 49., 327-334; and Plant Soil 1973, 28 / 605-619 teach the use of aqueous acetic acid or ammoniu acetate solutions as extractants. This method resulted in only slight leaching of metals from the soil. EP .278,328 (1988); Environ. Prog. 1990, 9 , 79-86; EP 377,766 (1990); and Chemiker-Zeitung 1982, 106. 289-292 teach the use of strongly acidic leachant solutions such as HC1. This method leads to substantial (ca. 30%) dissolution of soil components and requires extensive basification of each HC1 extract and/or the washed soil. DE 3,703,922 and DE 3,705,519 teach that isolation of the metal values is often impossible due to the metals having been precipitated as sulfides. EP 291,746 and SU 1,444,377 teach that complete separation of the soil and aqueous phases in an extraction process is difficult. J. Indian Chem. Soc, Sect. A 1982, 21A, 444-446; Hydrometallurgy 1987, 17, 215- 228; Nippon Kinzoku Gakkaishi, 1978, H, 1007-1012; Hydrometallurgy, 1985, 14, 171-188; J. Indian Chem. Soc. 1985, 62., 707-709; J. Anal. Chem. USSR, 1983, 3_8, 630-635; J. Inorg. Nucl. Chem. 1970, 3_2., 3667-3672; Russ. J. Inorg. Chem. I960, 5, 906; I. M. M. Bull. 1961, 70/ 355 and SU 710,487 teach the use of carboxylic acids such as fatty acids or Versatic™ acids for extraction of certain metals in standard liquid ion exchange processes. "The Theory and Practice of Ion Exchange: Proceedings of an International Conference," Cambridge, July 1976, Streat, M. ed. , Soc. of Chemical Industry: London, 1976, 38.1-38.7; Trans. Instn. Min. Metall. (Sect. C: Mineral Process. Extr. Metall.), 1974, 83 ./ C101-104; Trans. Instn. Min. Metall. (Sect. C: Mineral Process. Extr. Metall.), 1979, 88 / C31-35; "Usin Solvent-Impregnated Carbon to Recover Copper from Oxidize Mill Tailings," Rep. of Invest., USDI, Bur. Mines, No. 8966, 1985, pp 7 teach the use of solid-supported io exchange reagents to remove copper from clarified solution and from a slurry of oxidized mine tailings. Hydrometallurgy, 1982, 8. / 83-94; J. Chem. Tech. Biotechnol. 1981, 3_1, 345-350; Proc. - Indian Acad. Sci., Chem. Sci. 1988, 100. 359-361; Proc. - Indian Acad. Sci., Chem. Sci. 1988, 100, 455-457 teach the use of LIX™ 34, LIX™ 622, LIX 51, LIX™ 54, LIX™ 70, and Kelex™ 100 as extractants for lead from aqueous feeds, but only at more basic pHs than with the carboxylic acids extractants mentioned above. "ISEC '86 Int. Solv. Extract. Conf., Preprints, Vol. II," 1986, 19-26; and Hydrometallurgy 1985, 14. / 287-293 teach the use of diethylhexylphosphoric acid as a lead extractant under acidic conditions, but the S-shaped isotherm prohibits reducing the Pb concentration in the aqueous feed down to very low levels. Separation Science 1971, 6, 443- 450 teaches the extraction of metals from aqueous solutions by SRS-100, a high molecular weight synthetic carboxylic acid. Various soil removal processes which include the use of mineral acids, bases, surfactants, and sequestering agents are reviewed in International Conf. on New Frontiers for Hazardous Waste Management, Sept., 1987; The Fourth Environ. International Conf. 1983, 856-895; and Environmental Progress 1990, 9., 79-86. EP 402,737 teaches that heavy metals are dissolved out of sludge by strong mineral acid, and that the resulting mineral acid solution containing the heavy metals is treatable with a heavily alkaline solution containing flocculent and foaming agent. EP 278,328 teaches a process of extracting heavy metals from contaminated soils by treating the soils with a number of successive acid extractions in a counter-current fashion and precipitating the heavy metals from the recovered acid solutions. DE 3,742,235 teaches removal of heavy metals from contaminated soils by treating the soils with a 2-40 wt. % EDTA solution having a pH of about 6. U.S. 4,824,57 teaches an improved process for the purification of a impure aqueous solution containing heavy metal ions whic comprises passing the impure solution through a bed o activated alumina absorbent. U.S. 4,746,439 teaches process for the decontamination and removal of at least on of silver, lead, chromium(III) , zinc, or nickel ions fro aqueous waste streams by contacting the contaminated wast water at a pH of from 4 to 6 with an alkaline eart silicate solid having a surface area in the range of about 0.1-1000 m 2 /g. U.S. 4,883,599 teaches removal of metals from aqueous solutions by passing the solutions through an ion exchange material which consists essentially of sulfhydrated cellulose. Mercury contamination is a particularly difficult and insidious type of contamination to remediate because of the prevalence and interconvertability of ionic and elemental forms of mercury within a single site by natural weathering action as well as biological redox mechanisms. M. Meltzer, et al. [Pollution Technology Reviews, No. 196, Noyes Data Corp, Park Ridge, NJ, 1990, p. 373] teaches that water soluble and insoluble ionic mercury compounds are bioavailable for reduction to mercury metal by bacterial action, including the highly insoluble mercuric sulfide. The conversion of elemental mercury into water soluble ionic forms is also biologically possible as well as conversion into volatile dimethyl mercury. All forms and compounds of mercury are toxic including elemental mercury. [ ■ •The Merck Index," 11 th Ed., Merck & Co., Inc., Rahway, NJ, 1989, p 5805; P.C. Bidstrup, "Toxicity of Mercury and its Compounds," Elsevier, Amsterdam, 1964; L. Magos, Br. Med . Bull . 1975, 3JL, 241-5] The toxicity of the elemental form can not only be experienced by direct ingestion, but also by inhalation due to the relatively high vapor pressure of mercury, 2 x 10 "3 mm (25 °C) . The vapor pressure of mercury alone results in a concentration 200 times higher than the maximum allowed contentr tion , 0.01 ppm. Long exposure to mercury also produces a cummulative effect. A number o processes have been disclosed which claim to oxidativel dissolve elemental mercury and allow the reclamation of th metal. These processes all have disadvantages. Hot nitri acid solutions are known to oxidatively dissolve mercur while reducing nitrate to nitrogen oxides. [DE 3812986, 1989; DE 3703922, 1988] At room temperature an excess o nitric acid is required and extended periods of time. Under field conditions this will produce substantial quantities of volatile and regulated nitrogen oxides whic will require scrubbing before venting to the atmosphere. Additionally, nitrate contamination of groundwater remains a concern because of the large excess of nitric acid required. Hydrogen peroxide is also claimed .to oxidize mercury metal to mercuric ions. [USSR 431115, 1974] Catalysis by ferric or iodide ion is also reported. [EP 88- 118930, 1988] Hypochlorite in combination with hydrogen peroxide is also claimed. [JP Kokai 63156586, 1988] Hydrogen peroxide suffers the drawback in soil remediation use of being decomposed rapidly and irreversibly with manganese dioxide, a ubiquitous soil constitutent. [EP 88- 118930, 1988] This reaction produces useless oxygen gas and water. Peracetic acid at 80 °C has been used to produce mercuric acetate from mercury metal. Hydrogen peroxide in the presence of acetic acid was also successful. [US 2873289, 1959]. Hypochlorite oxidation of metallic mercury is known. Control of the pH and chloride ion concentration is required to ensure solubility of the mercuric ion. [US 3476552, 1969; Eng . Mining J. 1970, 171. 107-9]. Halogens, including chlorine, bromine, and chlorine with a bromide ion catalyst, are known to dissolve mercury metal and mercuric sulfide. [US 5013358, 1991; US 3424552, 1969; Chem . Abstr. 1990, 1_L4. / 232369c; Chem . Abstr. 1988, 109. 173955n] In soil remediation applications, this requires the use of highly toxic, volatile and corrosive materials in highly populated areas which makes this option less desirable than its use in remote mining locations. Additionally, halogens will react rapidly with organi humic matter in the soil to produce substantial amounts o chlorinated material, including chlorinated phenols. Thes chlorinated species would present difficulties wit regulatory agencies. Cyanide solutions are known t dissolve mercury metal to produce soluble mercuricyanid complexes. The danger of using cyanide solutions i populated areas limits the utility of this approach. In addition, thermal methods of removing mercury fro contaminated soil by distilling the metal are known. Thes suffer the drawback of the high cost of heating soil t approximately 600 °C. [DE 3928427, 1991; DE 3706684, 1987; "Treatment Technologies," US EPA, Office of Solid Waste, Government Inst. , Inc., 1990, p 17-1]. Methods for treatin metallic mercury and leaving it in the soil are also known. The long term acceptability of such practice is unknown. One example, ferric chloride oxidation of finely divided mercury metal, produces a thin layer of mercurous/mercuric chlorides which were reacted with a sulfide salt to produce a mercury particle reportedly coated with a layer of mercuric sulfide. This material could be further stabilized by known solidification techniques. [JP Kokai 81 07697, 1981; DE 3814684, 1989]. Amalgamation of metallic mercury with aluminum or iron deposited onto carbon is reported. The amalgam was claimed to be nonhazardous. [JP Kokai 73 75354, 1973; EP 342898, 1989]. Extraction of mercuric ions from the loaded leachate can be accomplished by a number of processes. [J. Ortega, J. Gutierrez, in "Recovery of Valuable Products from Wastes," Ortega et al. ed.] Recovery of mercury from concentrated solutions is also known by electrochemical reduction as disclosed in US 3,647,958 and D. Bender, F. Riordan, "Metal Bearing Waste Streams, Minimizing, Recycling and Treatment," M. Meltzer, et al. , ed. , Noyes Data Corp., Pollution Technology Review No. 196, Park Ridge, NJ, 1990, p. 298], and by reduction by iron as disclosed in US 5013358; by reduction by sodium borohydride [Morton Thiokiol, Inc., Ven Met Brochure , Ventron Division, 1984], and precipitation with sul ide is known [N.H. Feigenbaum, Ind. Wastes (Chicago) , 1977, 23. 324]. SUMMARY OF THE INVENTION It is an object of the present invention to efficiently remove heavy metals from contaminated soil or paint chips. The present invention achieves this objective by simple and concise processes. One process according to the invention removes heavy metals other than mercury including ionic forms thereof from the soil and comprises leaching or washing soil with a mild leachant. The leachant solution is comprised of an aqueous solution of an acid and a salt. The anion of the acid forms a water-soluble salt with all of the heavy metals which contaminate the soil. The salt component is comprised of at least one alkali metal, alkaline earth metal, or ammonium salt having one or more anions which also form a water-soluble salt with the heavy metals leached from the contaminated soil. The process can be modified by adding a second step. After the leachant solution has contacted the contaminated soil, a liquid phase containing dissolved heavy metal ions is formed and is. separated from the solids. The clarified liquid phase which remains after the solids have separated is treated with an extractant or a precipitant to remove the heavy metal ions. Where the extractant is adsorbed on an inert solid support or is a solid ion exchange material, the process can also be modified by accomplishing simultaneously both the leaching and extraction steps described above. Where the heavy metal to be removed from the soil is mercury, another process according to the invention comprises mixing soil and a liquid leachant composition which is an aqueous solution of (i) an acid whose anion forms a water-soluble salt with mercury; (ii) an alkali metal, alkaline earth metal, or an ammonium salt having one or more anions which form water-soluble salts with mercury, and (iii) an oxidant selected from the group consisting of a persulfate salt, nitric acid, and a halogen in such a manner as to disperse at least part of said soil in the leachant to form a liquid phase containing dispersed soil solids and for a period of time sufficient to transfer at least a portion of the mercury from the dispersed solids to a soluble mercury species in the liquid phase. Another process according to the invention is directed at removing lead, tin, or copper or mixtures thereof from paint chips which have been removed from copper, tin, or lead surfaces and/or paint chips which are comprised of paint which contains copper, tin, or lead or combinations thereof. Such process comprises contacting the paint chips with an aqueous acid leachant selected from the group consisting of formic acid, acetic acid, propionic acid, methanesulfonic acid, hydrochloric acid, nitric acid, and sulfuric acid for a period of time sufficient to transfer at least a portion of one or more of copper, tin, or lead from the paint chips to one or more soluble species in the leachant. The present invention is also directed toward a process for the complete remediation of mercury from contaminated soil which comprises the steps of: (l) mixing the soil and a liquid leachant composition which is an aqueous solution of (i) an acid whose anion forms a water-soluble salt with mercury; (ii) an alkali metal, alkaline earth metal, or an ammonium salt having one or more anions which form water- soluble salts with mercury, and (iii) an oxidant selected from the group consisting of a persulfate salt, nitric acid, and a halogen in such a manner as to disperse at least part of said soil in the leachant to form a liquid phase containing dispersed soil solids and for a period of time sufficient to transfer at least a portion of the mercury from the dispersed solids to a soluble mercury species in the liquid phase; (2) contacting the liquid phase with a metal such as aluminum, iron, or magnesium to remove the soluble mercury species from liquid phase. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a process flow- diagram for the simplest aspect of the process according to the invention which comprises a leaching step preceded by an optional classificatio step. Figure la is a process flow diagram for the firs modification of the process according to the inventio wherein the leaching step is continued after the optiona classification step, the soil or soil fines are separate from the leachant solution, and the heavy metals ar extracted from the clarified leachant solution. Figure lb is a process flow diagram for the secon modification of the process according to the inventio wherein the leaching step is continued after the classification step and combined with the extraction step wherein the extractant is a solid. The solid extractant is separated prior to the separation of the soil fines from the leachant solution. The solid extractant is stripped of extracted heavy metal ions, and the separated leachant solution is recycled for further leaching of contaminated soil. Figure lc is a process flow diagram for the operation of the second modification of the process according to the invention wherein the process of Figure lb is varied by recycling both the soil fines-leachant slurry and stripped extractant to leaching-extraction until an acceptable level of heavy metal removal has been attained. Figure 2 is a graph of the leaching effectiveness of various acetic acid solutions. Figure 3 is a graph of the leaching effectiveness of various hydrochloric acid solutions. Figure 4 is a graphic illustration of the effectiveness of various acetic acid/ammonium acetate solutions as leachants for lead. Figure 5 is a graphic illustration of the relative effectiveness of various solutions as leachants for lead. Figure 6 is a graphic illustration of the effectiveness of 5% acetic acid/2.5% acetate salt solutions in leaching lead from various forms of lead in clay matrices. DESCRIPTION OF THE PREFERRED EMBODIMENTS Other than in the operating examples, or whe otherwise indicated, all numbers expressing quantities ingredients or reaction conditions used herein are to understood as modified in all instances by the ter "about". For purposes of this invention, a heavy metal i a metal other than mercury and includes a transition metal a lanthanide, an actinide, thallium, lead, bismuth or tin The term soil means the upper layer or layers of the eart and includes sediment or silt below a body of water Contaminated soil is soil that contains unacceptably hig levels of heavy metals. Additionally, organic compound deleterious to the health and safety of plants, animals an humans such as hydrocarbons, chlorinated hydrocarbons, poly-chlorinated biphenyls, dioxin, high concentrations o herbicides and/or insecticides, and the like may b present. Unacceptably high levels of contaminants are thos levels which are higher than threshold levels set b governmental regulatory agencies. The term paint chip refers to a particle of solid paint film which had been applied to a surface as a liquid and subsequently cured to become a protective coating and then removed by some mechanical means such as by scraping, sandblasting, or blasting with plastic shot balls. The paint chips may or may not be mixed with other solid particles such as sandblasting or plastic shot residues and the like. An acid whose anion forms a water-soluble salt with a heavy metal according to the invention is any acid the anion or anions of which form a salt with a heavy metal as defined herein having a solubility in water which is equal to or greater than 10" 4 moles per liter. Examples of such acids include but are not limited to formic acid, acetic acid, propionic acid, methanesulfonic acid, hydrochloric acid, nitric acid, and sulfuric acid. A salt whose anion forms a water-soluble salt with a heavy metal according to the invention is any alkali metal, alkaline earth metal, or an ammonium salt having one or more anions which form water-soluble salts with a heavy metal as defined herein. An ammonium sal according to the invention is a salt having an ammonium io of the formula R 1 R 2 R 3 NH + wherein each of R lf R 2 , and R 3 i independently hydrogen, methyl, or ethyl. Examples of suc salts include but are not limited to those salts th cations of which are NH 4 + , Ca 2+ , Mg 2+ , Na + , K + , or Li + an the anions are acetate, Cl~, N0 3 " , or HS0 ~/S0 2 ". In its simplest aspect, the process according to th invention for removing heavy metals other than mercury fro soil can be carried out by mixing contaminated soil with leachant which is an aqueous solution comprised of: (a) a acid whose anion forms a water-soluble salt with the heav metal ions and (b) at least one alkali metal, alkalin earth metal, or ammonium salt having one or more anion which form water-soluble salts with the heavy metal ions. The contaminated soil and leachant are mixed together i any convenient manner such as by stirring the contaminate soil and the leachant solution together in a container. The ratio of soil to leachant will typically be 1 part b weight soil to from 2 to 10 parts by weight leachant. Preferably, the ratio of soil to leachant is 1 part by weight soil to from 2 to 5 parts by weight leachant. The soil will be contacted for a time sufficient to transfer at least a portion of the heavy metals to the leachant. The soil will typically be in contact with the leachant for up to 60 minutes. Soil containing elemental heavy metals may require longer leaching times to achieve dissolution. Optionally, at the start of the contacting period, a coarse solid phase of denser or larger soil particles, which is generally leached more rapidly than the soil fines, is separated by known size separation techniques, such as wet classification, centrifugal separation, hydrocyclone separation, or wet screening. Such techniques are further described in "Solids-Liquid Separation," Chem. Enq. f 1955, 62., 175-238, the entire contents of which is incorporated herein by reference. This operation classifies, or size segregates, the soil so that the remaining aqueous slurry contains only fine soil, silt and clay particles having diameter of generally less than 0.02 mm. Since the majorit of the heavy metal contaminants are associated with th soil fines, more extensive leaching of the soil fines i normally required than for the coarse soil components. I this way, the majority of the soil containing the coars constituents can be quickly freed of contaminants an disposed of, and the remaining soil fines can be furthe leached to more completely dissolve the contained heavy metals. The process according to the invention can be carried out at any temperature and will typically be carried out at ambient temperature. The minimum acid concentration in the leachant solution must be such that a pH of 7 or below is maintained during the leaching period in which the soil and/or the soil fines are contacted by the leachant solution. The maintenance of the pH of the leachant solution can be accomplished by intermittent addition of the acid to the solution or by continuous addition of the acid to the solution. The method of addition is not critical as long as the pH is maintained below 7. While the acid concentration can be any concentration required to maintain the pH at or below 7, the maximum acid concentration in the leachant solution will typically be about 2 moles per liter. In cases where the acid is a weak acid such as acetic acid the preferred concentration is in the range of 1-10 wt % and more preferably, in the range of 1-5 wt %. In cases where the acid is a strong acid such as hydrochloric acid, the preferred concentration is in the range of 0.01-1 molar and more preferably in the range of 0.05-0.5 molar. The minimum salt concentration in the leachant solution will be typically 0.05% while the maximum salt concentration in the leachant solution will be about 20% by weight. A preferred salt concentration is within the range of 1-20 wt %. A more preferred salt concentration is within the range of 2- 10%. It is contemplated in this invention that the soil ca be contacted with leachant multiple times to obtai sufficient removal of the heavy metals. Liquid-soli separation of partially leached soil gives a liquid phase containing a portion of the total of the heavy metal ions originally present in the soil and a solid phase which can be recycled for further leaching with fresh or regenerated leachant. Contacting and separating soil and leachant can be done continuously or in a batch mode. Figure 1 is a process flow diagram for the simplest aspect of the process according to the invention, in which soil is agitated with the leachant. The total time required to leach the heavy metals from the soil or soil fines and will typically take about 60 minutes or less. Optionally, the leaching step may be preceded by a classification step in the presence of the leachant to wash and remove a coarse fraction of soil. After the leaching step, the soil fines can optionally be separated from the leachant in the solid/liquid separation step. The soil or clay/humus soil fines may be disposed of if they are sufficiently free of heavy metals or they may be subjected to further leaching. Figure 2 illustrates the high degree of effectiveness of a mild (pH = 4) leachant, namely acetic acid plus ammonium or calcium acetate for leaching lead oxide from a clay matrix. Figure 3 illustrates the degree of effectiveness of a lower pH leachant, 0.1 M hydrochloric acid plus ammonium or calcium chloride for leaching lead oxide from a clay matrix. The novel leachants are substantially and surprisingly more effective than acetic acid or hydrochloric acid alone, ammonium or calcium acetate alone or with other additives as shown in Figure 3 and Figure 4. The novel acetic acid based leachants clearly leach more lead from contaminated soil faster than even the best hydrochloric acid based leachants as shown by curves repeated in Figure 5. The acetic acid based leachants are also especially useful because they dissolve Pb metal at pH = 4-7 as shown in Figure 6. Thus, the repetitive use of the acetic acid/acetate-based leachant is very efficient and effective at removing lead. from soi constituents. The process can be modified by adding subsequent liquid-solid separation and heavy metal recovery steps. Accordingly, in this first modification of the process according to the invention, the leaching step as described above is followed by the steps of separating the liquid leachant from the solid soil particles by any liquid-solid separation technique such as settling, filtering or centrifuging, and recovering the dissolved heavy metal from the separated liquid leachant by contacting with a water- insoluble extractant or a precipitant in order to remove the heavy metal ions. When a precipitant is used to remove the heavy metal ions the choice of the precipitant will depend upon the nature of the heavy metal contaminants and can be readily made by those skilled in the art. The use of such precipitants for aqueous waste solutions is described in "Treatment Technologies," Office of Solid Waste, U.S. EPA, Govt. Inst. , Inc., 1990. Typically, the precipitants will be calcium hydroxide, sodium hydroxide, sodium carbonate, sodium sulfide or sodium dimethyldithiocarbamate. Such precipitants will typically be used in stoichiometric excess to the heavy metals in the leachant solution when the leachant is not recycled back to the leaching step. The water insoluble extractant can be: (a) a co plexing agent for the heavy metal ions which is either dissolved in a water-immiscible solvent, adsorbed on an inert, solid support or adsorbed on a membrane support; (b) an ion exchange resin or an ion selective membrane; or (c) a solid adsorbent material. Examples of complexing agents which can be used as extractants include but are not limited to: carboxylic acids, such as Versatic™ 911 (Shell) , Neodecanoic™ acid (Exxon) or alpha-bromolauric acid; phosphorus acids, such as di-2-ethylhexylphosphoric acid, Cyanex™ 302 (Cyanamid, bis(2, 2, 4,4- trimethylpentyl)monothiophosphinic acid) ; phosphoru esters, such as tributyl phosphate or. dibuty butylphosphonate; phosphine oxides, such a trioctylphosphine oxide; phenolic oxi es, such as LIX™ 84 (Henkel, 2-hydroxy-5-nonylacetophenone oxime) or LIX™ 860 (Henkel, 5-dodecylsalicylaldehyde oxime) ; beta-diketones; such as LIX™ 54 (Henkel, l-phenyldecan-l,3-dione) or LIX™ 51 (Henkel, l-(p-dodecylphenyl)-4,4,4-trifluorobutan-1,3- dione; amines, such as trilaurylamine or trioctylamine; quaternary ammonium salts, such as Aliquat™ 336 (Henkel, tricaprylammonium chloride); and 8-hydroxyquinolines, such as LIX™ 26 (Henkel, 7-dodecenyl-8-hydroxyquinoline) . The preferred extractants are saturated, linear and branched carboxylic acids having from 7 to about 30 carbon atoms. Particularly preferred carboxylic acids are Neodecanoic™ acid (Exxon) and Versatic™ acids (Shell) . Examples of water immiscible solvents for dissolving the extractants are the aliphatic and aromatic hydrocarbons having flash points of 150 °F and higher and solubilities in water of less than 0.1% by weight. These solvents are also essentially non-toxic and chemically inert and the costs thereof are currently within practical ranges. Representative commercially available solvents include but are not limited to: Kermac 470B (an aliphatic kerosene available from Kerr-McGee—Flash Point 175 °F) , Chevron Ion Exchange Solvent (available from Standard Oil of California—Flash Point 195 °F) , Escaid 100 and 110 (available from Exxon-Europe—Flash Point of «180 °F) , Norpar 12 (available from Exxon-U.S.A.—Flash Point 160 °F) , Conoco C-1214 L (available from Conoco—Flash Point 160 °F) , Aromatic 150 (an aromatic kerosene available from Exxon- U.S.A.—Flash Point 150 °F) and various other kerosenes and petroleum fractions available from other oil companies. The use of said water immiscible solvents to recover the heavy metal by solvent extraction is especially advantageous when the heavy metal extraction process is followed by bioremediation. Solid supports for insoluble extractants can be nonfunctionalized resin beads. Examples of nonfunctionalized resin beads are the Amberlite™ XAD series, XAD-2, XAD-4, XAD-7 produced by Rohm and Haas. Membrane supports are microporous polymeric films which may be imbibed with liquid extractants to selectively allow heavy metal ions to pass through. Such membranes are described in "Interphase Transfer Kinetics from Transport Measurements Through Supported Liquid Membranes", "ISEC '86 Int. Solv. Extract. Conf., Preprints, Vol. II," 1986, 255- 262, the entire contents of which are incorporated herein by reference. Extractants with a variety of functionalities can be adsorbed onto a solid support and used to extract heavy metals. The appropriate combination of extractant and solid support will depend on the metal to be extracted and the conditions desired for extraction and stripping and can be determined by one of ordinary skill in the art. One method of determining the appropriate combination for a particular application would be to select an extractant which shows the desired characteristics in liquid-liquid extraction, imbibing that extractant onto a candidate solid support, and evaluating its extraction and stripping performance with a representative leach solution containing the heavy metal to be extracted. The water insoluble extractant can be an ion exchange resin which will exchange another ion or ions for the heavy metal ions. The functionality which can be used on the ion exchange resin will depend on the heavy metal to be extracted, the presence of other ions, and the pH of the aqueous phase. Examples of representative functionalities include sulfonic acid, carboxylic acid, tertiary amine, quaternary ammonium, and chelating groups such as amino- diacetic acid. Such ion exchange resins are described in "Ion Exchangers, Properties and Applications," K. Dorfner, Ann Arbor Sci. Publ. , Ann Arbor, MI, 1972 and "Ion Exchange," F. Helfferich, McGraw-Hill, NY, 1962 and their use is known to those skilled in the art. Ion selective membranes are described in "Encyclopedi of Chemical Technology", Kirk-Othmer, 8., 727-9, the entir contents of which are incorporated herein by reference. The solid adsorbent material can be coal, carbon, o crumb rubber. Coal is particulate bituminous, sub bituminous, lignite or peat having a particle size o greater than about 16 mesh. Carbon is particulate carbon o activated carbon having a particle size greater than abou 16 mesh (1.00 mm). Commercially available examples havin a mesh size of 6 x 16 are Calgon type GRC-22™, GRC-20™ Norit-RO™, and Norit-C™. The use of coal and carbon fo heavy metal extraction is described in Water Research 1982 16, 1113-1118; Water Research 1986, __0, 449-452; and Wate Research 1982, _L6, 1357-1366, the entire contents of whic are incorporated herein by reference. Crumb rubber i particulate rubber from recycled tires having a particl size of greater than about 16 mesh. The use of crum rubber as a heavy metal extractant is described in Wate Research 1981, _L5, 275-282, the entire contents of which i incorporated herein by reference. Figure la is a process flow diagram of the firs modification of the process according to the invention. I the first step, soil is mixed with a leachant. Optionally, a prior size classification can be conducted in which th coarse particles which are removed are substantially fre of heavy metal ions and are returned to the earth as clean fill. The soil or soil fines, which remain suspended as a slurry in step 2, and the leachant are further mixed together with the leachant in step 3 until the heavy metal ions are transferred from the soil or soil fines to the leachant as indicated by an analysis of a sample of the fines such as by atomic absorption spectroscopy. The time required to leach the heavy metals from the soil fines will typically be about 60 minutes or less. The soil or soil fines are then separated from the leachant in the solid/liquid separation step 4. The soil or clay/humus soil fines may be disposed of if they are sufficiently free heavy metals or they may be returned to step 3 for furth leaching. The liquid phase which results from t solid/liquid separation step contains dissolved heavy met ions. This heavy metal-containing leachant is th extracted in step 5 with a solid or liquid extractant t remove the dissolved heavy metal ions. The heavy metal loaded extractant is stripped by washing with strong aci to remove the heavy metals. The stripped extractant is the reused in the extraction step and the regenerated leachan is returned to the classification or leaching steps Alternatively, the soil may be preclassified by anothe technique and only the soil fines leached, or the soil ma be leached without classification. The amount of extractant and mode of extraction ar chosen so that the ion exchange capacity of the extractan or the adsorption capacity of the adsorbent for heav metals is greater than the amount of heavy metals to b extracted. Thus in a single, batchwise contact of heav metal containing leachant and extractant, an extraction or adsorption agent with an excess capacity for extraction or adsorption would be present. A preferred embodiment of the process according to the invention comprises mixing contaminated soil comprised of coarse and fine particles with an aqueous solution comprised of (a) an acid whose anion forms a water-soluble salt with the heavy metal ions and (b) at least one alkali metal, alkaline earth metal, or ammonium salt having one or more anions which form water-soluble salts with the heavy metal ions to produce a liquid slurry phase and a coarse solid soil phase. The coarse solid phase is removed by classification, and the liquid slurry phase continues to be leached. The liquid slurry phase is then subjected to a liquid-solid separation to produce a clarified liquid phase containing at least a portion of the heavy metals and a solid phase containing the soil fines. The clarified liquid phase is then contacted with a water-insoluble extractant dissolved in a water-immiscible solvent, a water-insolubl extractant adsorbed on an inert solid support, a adsorbent, or an ion exchange resin to remove the heav metals from the clarified liquid to produce regenerate leachant which is then returned for further leaching o contaminated soil. The solid phase containing the soi fines may be returned to further leaching with fresh o regenerated leachant. The leaching and liquid-soli separation of the soil fines is repeated until the heav metal contaminants in the soil fines have been reduced t the desired levels such as those prescribed by state an federal regulatory agencies. In another preferred embodiment, the aqueous leachan is comprised of acetic acid and an acetate salt of a alkaline earth metal or an ammonium ion as defined herein, and the extractant is activated carbon which removes the heavy metal ions from the liquid phase. The heavy metal ions are adsorbed by the carbon and can subsequently be removed from the carbon complex by washing with a strong acid. The heavy metals are then present in concentrated form in an acid solution for further isolation or processing. In a second modification of the process according to the invention, both steps of leaching and contacting with a solid extractant as set forth herein are accomplished simultaneously. Since contacting the soil one time with a leachant may remove less than all of the heavy metals present in the soil sample, repeated contacts of soil with leachant will often be needed to sufficiently remove the metal ions. Therefore, this second modification of the process according to the invention comprises carrying out the leaching and extracting steps simultaneously by mixing contaminated soil fines simultaneously with a leachant component and a water-insoluble solid extractant component as disclosed herein. In this second modification the soil must be classified to the extent that the remaining soil fines are separable from the solid extractant. The size difference between the soil particles and extractant particles should be at least a factor of two and preferably at least a factor of ten. The leachant component is an aqueous solution comprised of an acid whose anion forms a water-soluble salt with said heavy metal ions and at least one alkali metal, alkaline earth metal, or ammonium salt having one or more anions which form water-soluble salts with said heavy metal ions. The extractant component is either a water-insoluble extractant adsorbed on an inert, solid adsorbent material or adsorbed on a membrane support; an ion selective membrane; a solid adsorbent; or an ion exchange resin. A liquid slurry phase is thus obtained which contains the leachant component, soil fines, dissolved heavy metal ions, and the extractant component now containing at least a portion of the heavy metal in complexed form. This extractant component is separated from the liquid slurry phase to remove the extractant component loaded with the heavy metal ion complex. The loaded extractant component is then contacted with a stripping solution to remove the heavy metal in concentrated form, and regenerate the extractant for further contact with liquid slurry phase. The solid extraction component can be removed by passing the liquid slurry phase through a screen. A liquid slurry stream containing soil fines and heavy metals not removed in the first contact passes through the screen. This liquid slurry phase stream is then recycled back through, the leaching process with fresh or regenerated solid extractant component for a number of cycles sufficient to reduce the heavy metal concentration in the soil fines to the desired levels such as those prescribed by state and federal regulatory agencies. An advantage of this modification is the avoidance of expensive and time- consuming repetitive liquid-solid separation to produce clarified aqueous solution following each successive contact of leachant with the soil. This modification of the process according to the invention can also be carried out in a continuous manner by continuously removing the loaded extractant component from the liquid slurry phase and adding fresh or regenerated extractant component so that the continuous leaching of the soil fines allows high metal removal. The liquid slurry phase and the solid extractant may also be continuously advanced counter- currently to each other. Thus the heavy metals dissolve into the leachant and are directly complexed by the extractant component. This prevents buildup of high heavy metal concentrations in the leachant, and displaces the dissolution equilibrium toward completion, giving more rapid and complete removal of heavy metals from the soil. The resulting low concentration of heavy metals in solution permits the use of leachant acids and salts that might not otherwise have adequate solubility with the heavy metal, such as lead sulfate, but will give sufficient solubility for simultaneous leaching and extraction. The amount of solid extractant and mode of extraction are chosen so that the ion exchange capacity of the extractant or the adsorption capacity of the adsorbent for heavy metals is greater than the amount of heavy metals to be extracted. Thus in a single, batchwise contact of contaminated soil and extractant, an extraction or adsorption agent with an excess capacity for extraction or adsorption would be present. Alternatively, when the process is conducted continuously or with multiple contacts of the soil with extractant, the heavy metal concentration may initially be in excess of the capacity of the extractant present, but further contacting of the soil with fresh or regenerated extractant provides the excess capacity needed to remove substantially all of the heavy metal ions from the leachant solution. Figure lb is a process flow diagram for one aspect of the second modification of the process according to the invention wherein the extractant is a solid as set forth herein. In the first step the soil is classified with the leachant, in the second step the soil fines remain suspended as a slurry in the leachant and are further mixed together with solid extractant in step 4 to transfer the heavy metals ions from the soil fines via the leachant to the solid extractant. The total time for steps 1 and 4 is the time required to leach the metals from the soil fines and will typically take about 60 minutes or less. The solid extractant is then removed in step 5 by passing the leachant-soil fines-extractant slurry through a screen and recovering a regenerated leachant/soil fines slurry from which the soil fines are then removed in step 6 to produce a regenerated leachant stream for recycle to the classification/leaching step. The heavy metal-loaded solid extractant is stripped by washing with strong acid to remove the heavy metals. The stripped extractant in step 3 is then reused in the extraction step 4. Alternatively, the contaminated soil may be preclassified by another technique and only the soil fines leached in step 4. A process flow diagram for another aspect of the second modification of the process according to the invention is depicted in Figure lc. The aspect is similar to that depicted in Figure lb except that the regenerated leachant containing the soil fines and formed after step 5 is recycled back into step 4. Thus, the soil fines are continuously and repeatedly contacted by the leachant and solid extractant until the heavy metal ion content reaches an acceptable value. This continuous process is depicted by the solid arrows. After the heavy metal ion concentration reaches an acceptable level, the process continues through the hatched arrows wherein the cleaned soil fines are separated from the leachant and returned to the earth as fill. The heavy metal-free regenerated leachant can be returned to step 1 of the process. A preferred embodiment of the second modification of the process according to the invention is comprised of a leaching step which comprises contacting contaminated soil with, a leachant comprised of an acid whose anion forms a water-soluble salt with said heavy metal ions and at least one alkali metal, alkaline earth metal, or ammonium salt having one or more anions which form water-soluble salts with said heavy metal ions. The coarse solid phase of denser or larger soil particles is then separated by known. size separation techniques. This classifies, or size segregates, the soil so that the remaining first liquid slurry contains only fine soil particles, generally less than 0.02 mm in diameter. A carbon is added to produce a first liquid slurry phase and a coarse solid extractant phase. After sufficient time to transfer at least a portion of the heavy metals to the solid extractant, the first liquid slurry phase is passed through a screen having a mesh size of from about 80 (0.177 mm) to about 5 (4.00 mm) to remove the solid extractant phase which contains the heavy metal ion-carbon complex. A second liquid slurry phase stream containing soil fines and heavy metal ions not removed in the first contact results from this separation step and is recycled back to the leaching step. The solid extractant phase which remains on the screen is removed from the screen and the heavy metal ions are stripped by washing with a strong acid such as 3 M hydrochloric acid. The stripped extractant-solid is recycled back to the leaching step. The heavy metals are then present in an acid solution in concentrated form for further isolation or processing to recover the heavy metals. After a sufficient number of leaching cycles, the treated solid soil may be separated from the leachant and returned to the earth. The processes according to the invention are particularly effective in removing lead, zinc, cadmium, and bismuth from contaminated soil. The modified processes according to the invention can be even further altered by adding a bioremediation step at the end of the process. In other words, soil treated by the modified processes according to the invention in which the leaching step is followed by or carried out simultaneously with the extracting step or continuously with the extracting step can be freed of unwanted organic matter by subjecting the treated soil to bioremediation. Bioremediation is a process in which microorganisms are used to degrade organic contaminants to harmless by¬ products. An organic contaminant is any organic matter whose presence in soil renders the soil unfit for plant, animal or human contact or use. Examples of organic contaminants include hydrocarbon oils, gasoline, and heavier petroleum hydrocarbons; aromatic compounds such as benzene, toluene, xylene, and polynuclear aromatics; chlorinated hydrocarbons such as chlorinated benzenes, pentachlorophenol, and poly-chlorinated biphenyls; dioxin, herbicides and/or insecticides, and the like. Bioremediation may be accomplished by any method known to those skilled in the art such as by land treatment, bioreactors, and in-situ treatment. The use of bioremediation as a means of cleaning wastes of hazardous organic materials is described in the August 26, 1991 edition of Chemical and Engineering News, pages 23-34, the entire contents of which are incorporated herein by reference. Bioremediation is often hindered or even prevented when heavy metals are present due to their high toxicity. Thus, removal of heavy metals may be a necessary first step to allow bioremediation to take place. The use of acetic acid and acetate salt as the leachant is particularly preferred when heavy metal recovery is to be followed by bioremediation, since it leaves a residue of an only mildly acidic solution in the soil, and the residual acetate can act as a nutrient to the remediating microorganisms. In its simplest aspect, the process according to the invention which removes mercury from soil containing mercury can be carried out by mixing mercury-containing soil with a liquid leachant composition which is an aqueous solution of (i) an acid whose anion forms a water-soluble salt with mercury; (ii) an alkali metal, alkaline earth metal, or an ammonium salt having one or more anions which form water-soluble salts with mercury, and (iii) an oxidant selected from the group consisting of a persulfate sal nitric acid, and a halogen in such a manner as to disper at least part of said soil in the leachant to form a liqui phase containing dispersed soil solids and for a period time sufficient to transfer at least a portion of t mercury from the dispersed solids to a soluble mercur species in the liquid phase. An acid whose anion forms water-soluble salt with mercury according to the inventio is any acid the anion or anions of which form a salt wit mercury which has a solubility in water which is equal t or greater than 10 "4 moles per liter. Examples of such acid include but are not limited to formic acid, acetic acid propionic acid, methanesulfonic acid, hydrochloric acid nitric acid, and sulfuric acid. A salt whose anion forms water-soluble salt with mercury according to the inventio is any alkali metal, alkaline earth metal, or an ammoniu salt having one or more anions which form water-solubl salts with mercury as defined herein. An ammonium sal according to the invention is a salt having an ammonium io of the formula R 1 R 2 R 3 NH + wherein each of R 1# R 2 , and R 3 i independently hydrogen, methyl, or ethyl. Examples of suc salts include but are not limited to those salts th cations of which are NH 4 + , Ca 2+ , Mg 2+ , Na + , K + , or Li + an the anions are acetate, Cl " , N0 3 " , or HS0 4 " /S0 4 2" . Th contaminated soil and leachant are mixed together in an convenient manner such as by stirring the contaminated soi and the leachant solution together in a container. Th ratio of soil to leachant will typically be 1 part b weight soil to from 2 to 10 parts by weight leachant. Preferably, the ratio of soil to leachant is 1 part b weight soil to from 2 to 5 parts by weight leachant. Th soil will be contacted for a time sufficient to transfer at least a portion of the heavy metals and mercury to the leachant. The soil will typically be in contact with the leachant for up to 60 minutes. Optionally, at the start of the contacting period, a coarse solid phase of denser or larger soil particles, which is generally leached more rapidly than the soil fines, is separated by known siz separation techniques, such as wet classification, centrifugal separation, hydrocyclone separation, or we screening as set forth above. The mercury removal proces can be carried out at any temperature and will typically b carried out at slightly elevated (40-80°C) temperature. The minimum acid concentration in the leachant solution must be such that a pH of 7 or below is maintained during the leaching period in which the soil and/or the soil fines are contacted by the leachant solution. The maintenance of the pH of the leachant solution can be accomplished by intermittent addition of the acid to the solution or by continuous addition of the acid to the solution. The method of addition is not critical as long as the pH is maintained below 7. While the acid concentration can be any concentration required to maintain the pH at or below 7, the maximum acid concentration in the leachant solution will typically be about 2 moles per liter. In cases where the acid is a weak acid such as acetic acid the preferred concentration is in the range of 1-10 wt % and more preferably, in the range of 1-5 wt %. In cases where the acid is a strong acid such as hydrochloric acid, the preferred concentration is in the range of 0.01-1 molar and more preferably in the range of 0.05-0.5 molar. The minimum salt concentration in the leachant solution will be typically 0.05% while the maximum salt concentration in the leachant solution will be about 20% by weight. A preferred salt concentration is within the range of 1-20 wt %. A more preferred salt concentration is within the range of 2- 10%. The concentration of the oxidant in the leachant can range from about 1 eq to about 100 eq and will typically be from about 2 eq to about 50 eq. The preferred oxidant concentration will be from about 5 eq to about 25 eq. The oxidant is selected from the group consisting of a persulfate salt which includes an alkali metal or alkaline earth metal persulfate salt or, preferably, ammonium persulfate; nitric acid, and a halogen preferably bromine. The mercury removal process can be carried out in the sam manner as that described previously for the removal o heavy metals from soil and may also be accomplishe according to the process flow diagram as set forth i Figure 1. The process for removing mercury from soil can b modified by the addition of a cementation step afte leaching. The cementation step comprises contacting th liquid phase containing the leached, soluble mercur species liquid phase with aluminum, iron, or magnesium t remove the soluble mercury species from liquid phase. Th resulting process amounts to a complete remediation o mercury from the mercury-containing soil. Aluminum is th preferred metal for cementation. The amount of metal use in the cementation step is from about 1 eq to about 100 e based on 1 eq of Hg with the preferred amount being in the range of from about 5 eq to about 50 eq. The metal will be in contact with the liquid phase for a period of time from about 1 min to about 5 hr, preferably from about 10 min to about 1 hr. A cementation step can also be added to the process for removing heavy metals other than mercury from soil or from paint chips when the metals removed are reduceable by the cementing metal, examples of which are copper or lead. In such a case, the liquid phase containing the leached, soluble lead or copper species is contacted with aluminum, iron, or magnesium to remove the soluble mercury species from liquid phase. Aluminum is the preferred metal for cementation. The amount of metal used in the cemetation step is from about 1 eq to about 100 eq based on 1 eq metal with the preferred amount being in the range of from about 5 eq to about 50 eq. The metal will be in contact with the liquid phase for a period of time from about 1 min to about 5 hr, preferably from about 10 min to about 1 hr. The process according to the invention which removes lead, copper, or tin from paint chips containing one or more of said metals comprises contacting the paint chips with an aqueous acid leachant selected from the group consisting of formic acid, acetic acid, propionic acid, methanesulfonic acid, hydrochloric acid, nitric acid, and sulfuric acid for a period of time sufficient to transfer at least a portion of lead, copper, or tin or any combination thereof from the paint chips to one or more soluble species in the leachant. The process is carried out by contacting the paint chips with the leachant preferably by mixing the leachant and paint chips together in a vessel for a period of time from about 2 hr to about 12 hr. The ratio of leachant to paint chips or residue containing paint chips can be from about 2 to about 10 and is preferably from about 3 to about 5. The leaching process can be carried out at a temperature of from 10 β C to 100 °C or, preferably, from 20°C to 80°C. Most preferably, the paint chips will be reduced to a fine particle size by grinding or the like to increase the surface area of the chips and hence facilitate the removal of the lead, copper, or tin therefrom. The time required to remove the metal will vary with the nature of the paint chips and the amount of metal in the paint chips and can be easily determined by those having ordinary skill in the art. The paint chips can be contacted repeatedly by the leachant until the metal level is sufficiently reduced to meet a level set by law or some other standard. In one embodiment wherein paint chips containing lead are leached according to the process of the invention, the leaching is continued until the lead level is below the TCLP limit (Toxicity Characteristic Leaching Procedure) as determined by RCRA SW-846, Method 1311. The soluble lead or copper species or a combination thereof can be removed from the solution which remains after leaching by contacting the liquid phase containing the leached, soluble lead or copper species with aluminum, iron, or magnesium to remove the soluble mercury species from liquid phase. The following examples are meant to illustrate but not limit the invention. EXAMPLE 1 Dissolution of Lead Metal by Various Leachants Lead granules (0.20-0.30 g, 30 mesh) were stirred i an open 50 mL Erlenmeyer flask at 300 rpra with th following leachant solutions (25 mL) for 16 hrs, filtered dried, and the residual lead weighed. The percent lea dissolved is listed in Table 1. Table 1 Leachant % Pb Dissolved 5% HOAc 32 5% HOAc/5% HC1 9 10% HOAc 29 5% NH 4 0Ac 21 5% HOAc/2.5% NaOAc 36 5% HOAc/2.5% NH 4 OAc 43 The residual lead recovered from the acetic aci dissolution was not passivated by the treatment Subjecting the residual lead from the 5% HOAc treatment t two additional acetic acid treatments gave a further 35 and 32% dissolution. Longer exposure of the lead granule to acetic acid led to more complete dissolution (63 hr, 97 dissolution) . Results from similar experiments with lea and lead oxide are summarized in Figure 6. EXAMPLE 2 Dissolution of Lead Metal in a Matrix of Soil Constituent Lead granules (30 mesh) , the soil constituent (50 g) , and leachant (5% HOAc/2.5% NH OAc) were stirred in ope flasks for 66 hr before filtering and analyzing the filtrate for dissolved lead by atomic absorptio spectroscopy. The results are shown in Table 2. Table 2 The recovery of lead from the sand matrix was as high as i the absence of sand (compare with Example 1) . In th presence of clay, the recovery of lead was lower. Th lower recovery in the presence of clay is consistent with the strong metal binding capability of clays. By comparison, experiments using acetic acid alone or hydrochloric acid alone as in Figures 2 and 3 show virtually no recovery of lead from a clay matrix. EXAMPLE 3 Repetitive Leaching of a Lead Oxide/Clay Matrix by Various Acetic Acid Based Leachants Lead oxide (10 mg) , clay (2 g) , and leachant (10 mL) were stirred for 1 hr, centrifuged, the filtrate removed and analyzed, and fresh leachant added. The leachings were repeated three times. The results are shown in Figure 2. The acetic acid/ammonium acetate and acetic acid/calcium acetate combinations are especially effective. The effectiveness of various percentages of acetic acid and ammonium acetate are shown in Figure 4. The combination of acid and salt is surprisingly effective. Repetition of the experiment with 16, 22, 22, and 22 hr contact times gave similar results; 5% HOAc removed 12%, 5% HOAc/2.5% NH 4 0Ac removed 100%, and 5% HOAc/2.5% Ca(0Ac) 2 removed 85% of the Pb. Repetition of the experiment with 30 minute contact times gave results identical to those with 60 minutes contact times. EXAMPLE 4. Repetitive Leaching of a Lead Oxide/Clay Matrix by Various 0.1 M Hydrochloric Acid Based Leachants Lead oxide (10 mg) , clay (2 g) , and leachant (10 mL) were stirred for 1 hr, centrifuged, the filtrate removed and analyzed, and fresh leachant added. The leachings were repeated three times. The results are shown in Figure 3. The 0.1 M HC1/NH 4 C1 and 0.1 M HCl/CaCl 2 combinations are especially effective, but the rate at which Pb is removed is slower than with the acetic acid based leachants. EXAMPLE 5 Repetitive Leaching of Various Metal Oxides in a Clay Matrix by an Acetic Acid/Ammonium Acetate Leachant The metal oxide (10 mg) , montmorillonite clay (2 g) , and 5% acetic acid/2.5% ammonium acetate leachant (10 mL) were stirred for 1 hr, centrifuged, the filtrate remove and analyzed by atomic absorption, and fresh leachan added. The leachings were repeated three times. The cumulative percent metal leached is shown below. Bismuth and zinc are removed very efficiently. Cumulative % Metal Leached Leaching Contact EXAMPLE 6 Extraction of Lead from Leachant by Carbon A stock solution of 968 ppm lead was prepared in 5% acetic acid/2.5% ammonium acetate. A series of 6 dram vials were loaded with the stock solution (15 mL) and carbon (3 g) . The vials were mixed by rotation and aliquots removed for analysis. The lead remaining in each starting solution is tabulated below. Activated carbon efficiently adsorbs lead from the acetic acid/ammonium acetate leachant. % Available Lead adsorbed on C EXAMPLE 7 Acid Stripping of Lead from Carbon The lead bearing carbon (Calgon GRC-22, 3.00 g) from example 6 was rotated in a vial with 3M HC1 (10 mL) for 3 hrs. The acid solution was removed and analyzed by atomic absorption, and fresh hydrochloric acid was added and stripping continued another 2 hr. The carbon was stripped of 54% of the bound lead. EXAMPLE 8 Procedure for the Simultaneous Leaching and Extraction of Lead from Soil A sandy loam (3 g) containing lead oxide (10 mg) is sieved through a No.4 (2.00 mm) sieve and mixed with a particulate activated carbon (Calgon GRC-22, 2 g) in a vial. The 5% acetic acid/2.5% calcium acetate leachant (15 mL) is added, and the slurry mixed by rotation (50 rpm) for 2 hr. The carbon particles are removed by sieving through a No. 4 sieve. The isolated carbon particles are washed with water to remove traces of adhering soil fines, dried in an oven at 105 °C and after microwave digestion the solution is analyzed by atomic adsorption. The lead is thus removed from the soil matrix and adsorbed onto the carbon particles. EXAMPLE 9 Cementation by Aluminum This example shows the effectiveness of aluminum as a cementation agent for removing lead and copper from loaded leachants. A leachate solution (100 mL) containing Pb, Cu, Cd, Zn, and Fe in 5% acetic acid/5% sodium acetate was stirred with crushed aluminum foil pieces (1.00 g) in an open beaker. Aliquots (5 mL) were removed periodically to monitor the cementation of heavy metal ions by the aluminum, filtered and subjected to ICP (Inductively Couple Plasmid Spectroscopy) analysis. The results, which are given in Table 3, show that aluminum successfully removed 99% or more of the copper and lead ions by reduction to insoluble elemental copper and lead. Table 3. EXAMPLE 10 Leaching of Lead From Paint Chips in Sandblasting Waste a Room Temperature Sandblasting waste, sieved to a <2.00 mm fraction, contained sand, paint chips, and fines. The waste (2.00 g) and leachant (10.0 mL) were loaded into a polyethylen centrifuge tube, capped and shaken for 2 hr at roo temperature (20-22 β C) . The tube and contents wer centrifuged to give a solid pellet and leachant. Th leachant was removed by pipette and weighed. The soli pellet was contacted again with fresh leachant. Thi contacting, centrifuging and replacement with fres leachant was repeated a total of 5 times. The leachates were filtered (<0.45 μm) and analyzed by ICP for lead. The final treated solids were digested by the EPA acid digestion method and analyzed for lead. The results are shown in Table 4 for three leachants. The results indicate that at room temperature after five contacts partial lead removal (58-79%) from the waste was achieved. Table 4. Leaching of Waste Sandblasting Sand (<2.00 am) with Vari Leachants Temperature = 22-25 *C Based upon the total Pb detected in leachant plus Pb retained in sand as determined by nitric acid digestion. 2 Based upon nitric acid digestion of treated sand. 3 Leachant: 1 = 5% acetic acid/5% calcium acetate 2 = 0.1 M HCl/5% calcium chloride 3 = 0.5 M HCl/5% calcium chloride. EXAMPLE 11 Leaching of Lead From Paint Chips in Sandblasting Waste a 60°C The procedure described in Example 10 above was repeated at 60 °C. The agitation was accomplished by magnetic stirring while heating in a water bath. The results are shown in Table 5 and show that the lead removal was much higher (87-96%) than in the corresponding experiments at room temperature. Table 5. Leaching of Waste Sandblasting Sand (<2.00 mm) with Variou Leachants Temperature = 60 °C 1 Based upon the total Pb detected in leachant plus Pb retained in sand as determined by nitric acid digestion. 2 Based upon nitric acid digestion of treated sand. 3 Leachant: 1 = 5% acetic acid/5% calcium acetate 3 = 0.5 M HCl/5% calcium chloride 4 = 20% methanesulfonic acid. EXAMPLE 12 Leaching of Mercury from Soil Mercury metal (10-12 mg) was accurately weighed and mixed with clean soil (2.00 g, Goldridge Sandy Loam, Russian River Valley, CA) in a 50 mL rounded bottom flask equipped with a magnetic stirrer, condenser, and thermocouple. The mercury amended soil was stirred with 5% acetic acid/5% calcium acetate (10 mL) containing ammonium persulfate (10 and 25 eq.) at 60 °C for 1 hr. The resulting soil slurry was quantitatively transferred to a 50 mL polyethylene centrifuge tube, centrifuged, and the supernate decanted and analyzed. The remaining soil was leached with 5% acetic acid/5% calcium acetate solution (10 mL) , centrifuged, and the supernate decanted five times. All supernates were analyzed for mercury by ICP, and the remaining soil was acid digested (EPA Method 3050) to determine the residual mercury concentration in the treated soil. The results are shown in Table 6. On y t e rs contac con a ne ox an p us eac ant. ema n ng contacts were done with leachant only. EXAMPLE 13 Cementation of Mercury by Aluminum Two solutions of mercuric chloride in (a) 5% acetic acid/5% calcium acetate and (b) 0.1 M HCl/5% calcium chloride were prepared, approximately 350 ppm Hg. A portion of each solution (25 mL) was stirred with crushed aluminum foil pieces (25 mg) under nitrogen. Aliquots (5 mL) were removed periodically to monitor the cementation of the mercuric ion by the aluminum, filtered and subjected to ICP analysis. The results are in Table 3. It is readily apparent that aluminum successfully removed the mercuric ion by reduction to insoluble elemental mercury or reduction and amalgation to excess aluminum. Table 7. EXAMPLE 14 Electrovinning of Lead-Containing Leachant The leachate was produced by mixing 300g of soil (21,000 ppm of Zn; 4,500 ppm of Pb) with 3L of a 5%HOAc/5%NaOAc solution. The mix was put on an Eberbach tableshaker for 1.5 hrs and then allowed to settle over night. The next day the supernatant was decanted off: analysis indicated a leachate Pb concentration of 215 ppm and a Zn concentration of 1,7.70 ppm. An electrowinning cell with the following materials and dimensions was used: four aluminum cathodes (2.9"w x 3.5"h- total area of 81.2 in five titanium anodes (2.0"w x 3.0"h- expanded metal electrowinning cell- liquid dimensions of 2.6" x 3.5" 7.0"1, for a total volume of 64 in 3 =1054 ml; a leacha reservoir of 2L; tubing of 1/4" ID. The plates were plac in alternating fashion with a distance of 1/2" betwe anodes and cathodes. 2L of the above leachate was recycl through the system via a FMI pump and a rate of 120ml/mi Electric current was established at 2.25V and at whi point gas evolution was noted; voltage was then reduced 1.75V and maintained for 5 hrs. Aliquots were taken every hour and analyzed f Pb: Sample Resulting Pb levels lhr 216 2hr 172 3hr 140 4hr 118 5hr 99.5

Claims: What is claimed is: 1. A process for removing heavy metals from contaminated soil which comprises mixing said soil and a liquid leachant composition which is an aqueous solution of (i) an acid- whose anion forms a water-soluble salt with said heavy metals and (ii) an . alkali metal, alkaline earth metal, or an ammonium salt having one or more anions which form water-soluble salts with said heavy metals, in such a manner as to disperse at least part of said soil in the leachant to form a liquid phase containing dispersed soil solids and for a period of time sufficient to transfer at least a portion of the heavy metals from the dispersed solids to a soluble species in the liquid phase. 2. The process of claim 1 wherein said acid is acetic acid. 3. The process of claim 2 wherein the concentration of said acetic acid is from about 1 to about 10 weight percent. 4. The process of claim 1 wherein said salt is an acetate salt of an alkali metal, alkaline earth metal or an ammonium acetate salt. 5. The process of claim 4 wherein the concentration of said acetate salt is from about 0.05 to about 20 weight percent. 6. The process of claim 1 wherein said leachant is comprised of acetic acid and an acetate salt of an alkali metal, alkaline earth metal or an ammonium acetate. 7. The process of claim 4 wherein said acetate salt is calcium acetate. 8. The process of claim 4 wherein said acetate salt is ammonium acetate. 9. The process of claim 1 wherein said leachant comprised of from about 1% to about 5% by weight of acet acid and from about 2% to about 10% by weight of calci acetate or ammonium acetate or a mixture of calcium aceta and ammonium acetate. 10. The process of claim 1 wherein said acid i hydrochloric acid. 11. The process of claim 10 wherein the concentration o said hydrochloric acid is from about 0.01 to about 1. molar. 12. The process of claim 1 wherein said salt is calciu chloride. 13. The process of claim 12 wherein the concentration o said calcium chloride is from about 0.05 to about 20 weigh percent. 14. The process of claim 1 wherein said salt is ammoniu chloride. 15. The process of claim 14 wherein the concentration o said ammonium chloride is from about 0.05 to about 2 weight percent. 16. The process of claim 1 wherein said leachant i comprised of from about 0.05 to about 0.5 mola hydrochloric acid and about 2% to about 10% by weight o ammonium chloride. 17. The process of claim 1 wherein said aqueous solution i comprised of from about 0.05 to about 0.5 mola hydrochloric acid and from about 2% to about 10% by weigh of calcium chloride. 18. A process for removing heavy metals from contaminate soil comprising the steps of: (1) mixing said soil and liquid leachant composition which is an aqueous solution o (i) an acid whose anion forms a water-soluble salt wit said heavy metals ions and (ii) an alkali metal, alkalin earth metal, or an ammonium salt having one or more anion which form water-soluble salts with said heavy metals, i such a manner as to disperse at least part of said soil i the leachant to form a liquid phase containing disperse soil solids; (2) maintaining the soil solids in th separated liquid phase containing the dispersed solids i dispersed form for a period of time sufficient to transfer at least a portion of the heavy metals from the dispersed solids to a soluble species in the liquid phase; (3) separating said dispersed solids from said liquid phase; and (4) contacting said liquid phase with an extractant to remove said heavy metals. 19. The process of claim 18 wherein step (4) is carried out by contacting said liquid phase with an extractant selected from the group consisting of: (a) a water insoluble extractant dissolved in a water-immiscible solvent; (b) a water insoluble extractant adsorbed on a water-insoluble solid support or on a membrane support; (c) an ion exchange resin or an ion-selective membrane; (d) a precipitating agent, and (e) coal, carbon, or crumb rubber. 20. The process of claim 18 wherein said acid is acetic acid. 21. The process of claim 20 wherein the concentration of said acetic acid is from about 1 to about 10 weight percent. 22. The process of claim 18 wherein said salt is an acetate salt of an alkali metal, alkaline earth metal or an ammonium acetate salt. 23. The process of claim 22 wherein the concentration said acetate salt is from about 0.05 to about 20 weig percent. 24. The process of claim 18 wherein said aqueous soluti is comprised of acetic acid and an acetate salt of alkali metal, alkaline earth metal or an ammonium acetat 25. The process of claim 22 wherein said acetate salt calcium acetate. 26. The process of claim 22 wherein said acetate salt ammonium acetate. 27. The process of claim 18 wherein said aqueous solutio is comprised of from about 1% to about 5% by weight o acetic acid and from about 2% to about 10% by weight o calcium acetate or ammonium acetate or a mixture of calciu acetate and ammonium acetate. 28. The process of claim 18 wherein said acid i hydrochloric acid. 29. The process of claim 28 wherein the concentration o said hydrochloric acid is from about 0.01 to about 1. molar. 30. The process of claim 18 wherein said salt is calciu chloride. 31. The process of claim 30 wherein the concentration o said calcium chloride is from about 0.05 to about 20 weigh percent. 32. The process of claim 18 wherein said salt is ammoniu chloride. 33. The process of claim 32 wherein the concentration o said ammonium chloride is from about 0.05 to about 2 weight percent. 34. The process of claim 18 wherein said aqueous solutio is comprised of from about 0.05 to about 0.5 mola hydrochloric acid and about 2% to about 10% by weight o ammonium chloride. 35. The process of claim 18 wherein said aqueous solutio is comprised of from about 0.05 to about 0.5 mola hydrochloric acid and from about 2% to about 10% by weigh of calcium chloride. 36. The process of claim 18 further comprising prior to said step (2) the step of separating said liquid phase containing the dispersed soil solids as prepared in said step (1) from any part of the soil which is not dispersed therein. 37. A process for removing heavy metals from contaminated soil comprising the steps of: (1) mixing said soil and a liquid leachant composition which is an aqueous solution of (i) an acid whose anion forms a water-soluble salt with said heavy metal ions and (ii) at least one alkali metal, alkaline earth metal, or ammonium salt having one or more anions which form water-soluble salts with said heavy metal ions, in such a manner as to disperse at least part of said soil in the leachant to form a liquid phase containing dispersed soil solids; (2) adding a solid extractant having a particle size at least twice as large as said dispersed soil solids to said liquid phase containing said dispersed soil solids to form a first dispersed phase; (3) maintaining the soil particles and the solid extractant in said first dispersed phase each in dispersed form for a period of time sufficient to transfer at least a portion of the heavy metals from the dispersed solids to an adsorbed species on said solid extractant; (4) separating said soli extractant from said first dispersed phase to form a second dispersed phase containing the dispersed solids i dispersed form; (5) stripping said heavy metals from said solid extractant to form a stripped solid extractant; (6) adding said stripped solid extractant to step (2) . 38. The process of claim 37 further comprising the step of adding said second dispersed phase formed in step (4) to step (2) and repeating steps (2), (3), (4), (5), and (6) 39. The process of claim 37 wherein said extractant is selected from the group consisting of: (a) a complexing agent for said heavy metal adsorbed on a solid support (b) an ion exchange resin and; (c) a solid adsorbent material. 40. The process of claim 39 wherein said extractant is a linear or branched carboxylic acid having from 7 to about 30 carbon atoms adsorbed on a support. 41. The process of claim 40 wherein said carboxylic acid is Neodecanoic™ acid or Versatic™ acid. 42. The process of claim 39 wherein said extractant is carbon. 43. The process of claim 37 wherein said acid is acetic acid. 44. The process of claim 43 wherein the concentration of said- acetic acid is from about 1 to about 10 weight percent. 45. The process of claim 37 wherein said salt is an acetate salt of an alkali metal, alkaline earth metal or an ammonium acetate salt. 46. The process of claim 45 wherein the concentration said acetate salt is from about 0.05 to about 20 weig percent. 47. The process of claim 37 wherein said aqueous soluti is comprised of acetic acid and an acetate salt of alkali metal, alkaline earth metal or an ammonium acetat 48. The process of claim 47 wherein said acetate salt calcium acetate. 49. The process of claim 47 wherein said acetate salt i ammonium acetate. 50. The process of claim 37 wherein said aqueous solutio is comprised of from about 1% to about 5% by weight o acetic acid and from about 2% to about 10% by weight o calcium acetate or ammonium acetate or a mixture of calciu acetate and ammonium acetate. 51. The process of claim 37 wherein said acid i hydrochloric acid. 52. The process of claim 51 wherein the concentration o said hydrochloric acid is from about 0.01 to about 1 molar. 53. The process of claim 37 wherein said salt is calciu chloride. 54. The process of claim 53 wherein the concentration of said calcium chloride is from about 0.05 to about 20 weight percent. 55. The process of claim 37 wherein said salt is ammonium chloride. 56. The process of claim 55 wherein the concentration said ammonium chloride is from about 0.05 to about weight percent. 57. The process of claim 37 wherein said aqueous soluti is comprised of from about 0.05 to about 0.5 mol hydrochloric acid and about 2% to about 10% by weight ammonium chloride. 58. The process of claim 37 wherein said aqueous soluti is comprised of from about 0.05 to about 0.5 mol hydrochloric acid and from about 2% to about 10% by weig of calcium chloride. 59. The process of claim 37 further comprising the step prior to step (2) , separating said liquid phase containi the dispersed soil solids as prepared in step (1) from an part of the soil which is not dispersed therein. 60. A process for removing heavy metals from contaminate soil comprising the steps of: (1) mixing said .soil and liquid leachant composition which is an aqueous solution o acetic acid and an acetate salt selected from the grou consisting of ammonium acetate, calcium acetate and mixture of ammonium acetate and calcium acetate in such manner as to disperse at least part of said soil in th leachant to form a liquid phase containing dispersed soi solids; (2) separating the liquid phase containing th dispersed soil solids as prepared in step (1) from any par of the soil which is not dispersed therein; (3) addin activated carbon having a particle size at least twice a large as said dispersed soil solids to said liquid phas containing said dispersed soil solids to form a firs dispersed phase; (4) maintaining the soil particles and th activated carbon in said first dispersed phase each i dispersed form for a period of time sufficient to transfe at least a portion of the heavy metals from the disperse solids to an adsorbed species on said activated carbon; separating said activated carbon from said first disper phase to form a second dispersed phase containing dispersed solids in dispersed form; (6) stripping s heavy metals from said activated carbon to form a strip activated carbon; (7) adding said stripped activated car to step (3) ; adding said second dispersed phase to s (3); and repeating steps (3), (4), (5), (6), and (7). 61. The process of claim 60 wherein the concentration acetic acid is from about 1% to about 5% by weight and concentration of said acetate salt is from about 2% about 10% by weight. 62. The process of claim 60 where the heavy metal remo is lead. 63. A process for removing mercury from mercury-containi soil which comprises mixing soil and a liquid leacha composition which is an aqueous solution of (i) an ac whose anion forms a water-soluble salt with mercury; (i an alkali metal, alkaline earth metal, or an ammonium sa having one or more anions which form water-soluble sal with mercury, and (iii) an oxidant selected from the gro consisting of a persulfate salt, nitric acid, and a halog in such a manner as to disperse at least part of said so in the leachant to form a liquid phase containing dispers soil solids and for a period of time sufficient to transf at least a portion of the mercury from the dispersed soli to a soluble mercury species in the liquid phase. 64. The process of claim 63 wherein said acid is aceti acid. 65. The process of claim 64 wherein the concentration o said acetic acid is from about 1 to about 10 weigh percent. 66. The process of claim 63 wherein said salt is an acet salt of an alkali metal, alkaline earth metal or ammonium acetate salt. 67. The process of claim 66 wherein the concentration said acetate salt is from about 0.05 to about 20 wei percent. 68. The process of claim 63 wherein said leachant comprised of acetic acid and an acetate salt of an alk metal, alkaline earth metal or an ammonium acetate. 69. The process of claim 66 wherein said acetate salt calcium acetate. 70. A process for the remediation of mercury contaminati in soil which comprises: (1) mixing soil and a liqu leachant composition which is an aqueous solution of (i) acid whose anion forms a water-soluble salt with mercur (ii) an alkali metal, alkaline earth metal, or an ammoni salt having one or more anions which form water-solub salts with mercury, and (iii) an oxidant selected from t group consisting of a persulfate salt, nitric acid, and halogen in such a manner as to disperse at least part said soil in the leachant to form a liquid phase containi dispersed soil solids and for a period of time sufficie to transfer at least a portion of the mercury from t dispersed solids to a soluble mercury species in the liqu phase; (2) contacting said liquid phase containing t leached, soluble mercury species with a metal selected fr the group consisting of aluminum, iron, and magnesium remove the soluble mercury species from liquid phase. 71. The process of claim 70 wherein said acid is acet acid. - 72. The process of claim 71 wherein the concentration said acetic acid is from about 1 to about 10 weig percent. 73. The process of claim 70 wherein said salt is an acetat salt of an alkali metal, alkaline earth metal or a ammonium acetate salt. 74. The process of claim 73 wherein the concentration o said acetate salt is from about 0.05 to about 20 weigh percent. 75. The process of claim 70 wherein said leachant i comprised of acetic acid and an acetate salt of an alkal metal, alkaline earth metal or an ammonium acetate. 76. The process of claim 75 wherein said acetate salt i calcium acetate. 77. The process of claim 70 wherein said metal is aluminum. 78. A process for removing copper, tin, or lead or combinations thereof from paint chips which comprises contacting the paint chips with an aqueous acid leachant selected from the group consisting of formic acid, acetic acid, propionic acid, methanesulfonic acid, hydrochloric acid, nitric acid, and sulfuric acid for a period of time sufficient to transfer at least a portion of one or more of copper, tin, or lead from the paint chips to one or more soluble species in the leachant. 79. A process for removing copper or lead or combinations thereof from paint chips comprising the steps of: (1) contacting the paint chips with an aqueous acid leachant selected from the group consisting of formic acid, acetic acid, propionic acid, methanesulfonic acid, hydrochloric acid, nitric acid, and sulfuric acid for a period of ti sufficient to transfer at least a portion of one or more copper or lead from the paint chips to one or more solub species to form a solution; (2) contacting said soluti with a metal selected from the group consisting aluminum, iron, and magnesium to remove the soluble copp or lead species or a combination thereof from liquid phas 80. The process of claim 78 wherein said acid methanesulfonic acid.

Inventors: CASSEL JONATHAN M, ELLIOTT DANA K, FRISTAD WILLIAM E, VIRNIG MICHAEL J, CASSEL, JONATHAN, M., ELLIOTT, DANA, K., FRISTAD, WILLIAM, E., VIRNIG, MICHAEL, J.
Applicants: COGNIS INC, COGNIS, INC.
Application year: 1992
Main classification: B09B3
IPC codes: B03B5, B09B3, B09C1, C01G13, C01G21, C22B1, C22B3, C22B7, C22B13, C22B15, C22B25, C22B43