Froth flotation of silica or siliceous gangue

Abstract: Silica and siliceous gangue are separated from desired mineral values, particularly iron and phosphate, by reverse froth flotation in the presence of an amine collector and an effective amount of an alkanol amine such as diethanol amine.

Description: This invention is related to reverse flotation processes wherein silica or siliceous gangue is floated. Flotation is a process of treating a mixture of finely divided mineral solids, e.g., a pulverulent ore, suspended in a liquid whereby a portion of the solids is separated from other finely divided mineral solids. e.g., silica, siliceous gangue, clays and other like materials present in the ore, by introducing a gas (or providing a gas in situ ) in the liquid to produce a frothy mass containing certain of the solids on the top of the liquid, and leaving suspended (unfrothed) other solid components of the ore. Flotation is based on the principle that introducing a gas into a liquid containing solid particles of different materials suspended therein causes adherence of some gas to certain suspended solids and not to others and makes the particles having the gas thus adhered thereto lighter than the liquid. Accordingly, these particles rise to the top of the liquid to form a froth. The minerals and their associated gangue which are treated by froth flotation generally do not possess sufficient hydrophobicity or hydrophilicity to allow adequate separation. Therefore, various chemical reagents are often employed in froth flotation to create or enhance the properties necessary to allow separation. Collectors are used to enhance the hydrophobicity and thus the floatability of different mineral values. Collectors must have the ability to (1) attach to the desired mineral species to the relative exclusion of other species present: (2) maintain the attachment in the turbulence or shear associated with froth flotation: and (3) render the desired mineral species sufficiently hydrophobic to permit the required degree of separation. A number of other chemical reagents are used in addition to collectors. Examples of types of additional reagents used include frothers, depressants, pH regulators, such as lime and soda, dispersants and various promoters and activators. Depressants are used to increase or enhance the hydrophilicity of various mineral species and thus depress their flotation. Frothers are reagents added to flotation systems to promote the creation of a semi-stable froth. Unlike both depressants and collectors. frothers need not attach or adsorb on mineral particles. Promoters and activators increase or enhance the effectiveness of other reagents such as collectors or depressants. Froth flotation has been extensively practiced in the mining industry since at least the early twentieth century. In the typical or direct flotation scheme, the valuable or desired mineral is floated away from the gangue material which is left in the tailings. In another type of flotation scheme called reverse flotation, the undesired mineral, such as silica or siliceous gangue is floated away from the valuable minerals which are left in the tailings. A wide variety of compounds are taught to be useful as collectors, frothers and other reagents in froth flotation. For example, in reverse flotation where silica or siliceous gangue is floated away from valuable minerals, amines such as simple primary and secondary amines, primary ether amines and ether diamines, tallow amines and tall oil fatty acid/amine condensates are generally accepted as useful collectors. Reagents useful as frothers include lower molecular weight alcohols such as methyl isobutyl carbinol and glycol ethers. The specific additives used in a particular flotation operation are selected according to the nature of the ore, the conditions under which the flotation will take place, the mineral sought to be recovered and the other additives which are to be used in combination therewith. US-A-2,177,985 discloses froth flotation processes in which the collector is an ester or ether of a quaternary ammonium-substituted alkanol or glycol. Specified processes include the separation of gangue from siliceous ores. Reference is made to the presence of additives such as other collectors, frothers, depressants, emulsifiers, dispersants, activators, deactivators, inhibitors and conditioners. Triethanol amine is included to exemplify amines in a list of numerous suitable additives. US-A-4,276,156 discloses the removal of gangue from siliceous phosphate ore by froth flotation in which the collector is a condensation product of (1) a fatty acid or fatty acid ester, (2) a hydroxyethylenediamine, and, optionally, (3) a mono-, di- or tri-ethanol amine. US-A-4,732,667 discloses froth flotation removal of silica and siliceous gangue from mineral values in the presence, as collectors, of both a primary amine and a nitrogen compound containing a methylene carboxylic acid, methylene phosphonic acid or ethylene phosphoric acid group. The primary amines can include an ether substituent but there is no reference to alkanol amines. It is recognized that the effectiveness of known reagents varies greatly depending on the particular ore or ores being subjected to flotation as well as the flotation conditions. One problem that is also recognized is that the amine collectors used to float silica frequently are not as selective to silica as desirable and also float the valuable mineral with the silica resulting in diminished recoveries of the desired minerals in the tailings. Thus, a need remains for more efficient methods of removing silica or siliceous gangue from valuable minerals in reverse flotation processes. The present invention is a process for the recovery of mineral values by reverse froth flotation comprising subjecting a particulate ore, which contains silica or siliceous gangue and is in an aqueous slurry, to froth flotation in the presence of an amine collector and at least one alkanol amine under conditions such that the silica or siliceous gangue is floated and the mineral values are left in tailings. Additionally, the froth flotation process of this invention utilizes frothers and other flotation reagents known in the art. The flotation process of this invention is useful in the recovery of various minerals, including oxide minerals, by reverse froth flotation. It is surprising that the use of a small amount of an alkanol amine with amine collectors results in enhanced performance by the amine collector. The reverse flotation process of this invention is useful in the recovery of mineral values from a variety of ores containing silica or siliceous gangue. An ore herein refers to the mineral as it is taken out of the ground and includes the mineral-containing species intermixed with gangue including the silica gangue. Gangue are those materials which are of little or no value and need to be separated from the mineral values. Examples of silica-containing oxide ores which may be treated using the collector of this invention preferably include iron oxides, nickel oxides, phosphorus oxides, copper oxides and titanium oxides. The treatment of iron-containing and phosphorus-containing ores is particularly preferred. Other types of oxygen-containing minerals having silica gangue which may be treated using the collector of this invention include carbonates such as calcite or dolomite and hydroxides such as bauxite. Various silica-containing sulfide ores may also be treated using the collector of this invention. Examples of sulfide ores which may be floated by the collector of this invention include those containing chalcopyrite, chalcocite, galena, pyrite, sphalerite and pentlandite. As will be recognized by one skilled in the art, various silica-containing ores may be treated by reverse flotation where the silica gangue is floated away from the desired mineral values. Examples of silica-containing oxide ores which may be treated using the collector of this invention are ores including cassiterite, hematite, cuprite, vallerite, calcite, talc, kaolin, apatite, dolomite, bauxite, spinel, corundum. laterite, azurite, rutile, magnetite, columbite, ilmenite, smithsonite, anglesite, scheelite. chromite. cerussite, pyrolusite, malachite, chrysocolla, zincite, massicot, bixbyite, anatase, brookite, tungstite, uraninite, gummite, brucite, manganite, psilomelane, goethite, limonite, chrysoberyl, microlite, tantalite and samarskite. One skilled in the art will recognize that the reverse froth flotation process of this invention will be useful for the processing of additional ores including oxide ores wherein oxide is defined to include carbonates, hydroxides, sulfates and silicates as well as oxides and sulfide ores. In addition to the flotation of ores found in nature, the reverse flotation process of this invention is useful in the flotation of oxides and sulfides from other sources. For example, the waste materials from various processes such as heavy media separation, magnetic separation, metal working and petroleum processing often contain oxides and/or sulfides having silica or siliceous gangue that may be recovered using the reverse flotation process of the present invention. The collectors useful in the flotation of silica in the process of this invention are known in the art and include amine collectors having at least twelve carbon atoms. Examples of such collectors include primary amines, secondary amines, primary ether amines and ether diamines, tallow amines and tall oil fatty acid/amine condensates. Examples of such collectors include 3-nonyloxy-propanamine; 1,3-propanediamine, N-tridecyloxy-3,1-propanediyl-; the condensate of diethylenetetraamine and tall oil fatty acid; C₁₆-C₁₈ tallow amine, decylamine, dihexyl amine and the condensate of an excess of fatty acids with diethanolamine. Alkanol amines are useful in this invention to enhance the flotation of silica in reverse flotation. The alkanol amines correspond to the formula (R) x NH (3-x) wherein x is from one to three and R is separately in each occurrence a C₁₋₆ hydroxyalkyl. Preferably, the alkanol amine is ethanol amine, diethanol amine, triethanol amine, propanol amine, isopropanol amine, butanol amine, isobutanol amine or mixtures thereof. The alkanol amines useful in the practice of this invention are available commercially. As will be recognized by one skilled in the art, commercially available alkanol amines will have varying degrees of purity. For example, commercially available diethanol amine may contain varying amounts of ethanol amine and/or triethanol amine. Such alkanol amines are suitable in the practice of the present invention. The alkanol amines are added prior to the addition of the collector and may be added directly to the float cell or may be added to the grinding stage. The amine collector can be used in any concentration which results in the flotation of a sufficient amount of silica or siliceous gangue to give the desired recovery of the desired metal values in the flotation tailings. In particular, the concentration used is dependent upon the particular mineral to be treated, the grade of' the ore to be subjected to the froth flotation process and the desired quality of the mineral to be recovered. Additional factors to be considered in determining dosage levels include the amount of surface area of the ore to be treated. As will be recognized by one skilled in the art, the smaller the particle size, the greater the amount of collector reagents needed to obtain adequate recoveries and grades. Preferably, the concentration of the collector is at least 0.001 kg/metric ton of ore, more preferably at least 0.005 kg/metric ton. It is also preferred that the total concentration of the collector is no greater than 5.0 kg/metric ton and more preferred that it is no greater than 2.5 kg/metric ton. It is more preferred that the concentration of the collector is between 0.005 kg/metric ton and 0.100 kg/metric ton. It is generally preferred to start at the lower concentration range and gradually increase the concentration to obtain optimum performance. The concentration of the alkanol amines useful in this invention is at least that amount sufficient to show a decrease in the amount of valuable mineral inadvertently floated with the silica or siliceous gangue. This amount is preferably at least 0.001 kg/metric ton of dry solids and no greater than 1.5 kg/metric ton. A more preferred concentration is between 0.01 kg/metric ton and 0.10 kg/metric ton. It has been found advantageous in the recovery of certain minerals to add the collector to the flotation system in stages. By staged addition, it is meant that a part of the total collector dose is added; froth concentrate is collected; an additional portion of the collector is added; and froth concentrate is again collected. This staged addition can be repeated several times to obtain optimum recovery and grade. The number of stages in which the collector is added is limited only by practical and economic constraints. Preferably, no more than six stages are used. In addition to the amine collectors and alkanol amines useful in this invention, other conventional additives may be used in the flotation process, including other collectors. Examples of such additives include depressants and dispersants. In addition to these additives, frothers may be and preferably are also used. Frothers are well-known in the art and reference thereto is made for the purposes of this invention. Non-limiting examples of useful frothers include C₅₋₈ alcohols, pine oils, cresols, C₁₋₆ alkyl ethers of polypropylene glycols, dihydroxylates of polypropylene glycols, glycol fatty acids, soaps, alkylaryl sulfonates and mixtures thereof. The pH in flotation systems may be controlled by various methods known to one skilled in the art. A common reagent used to control pH is lime. However, in the practice of this invention, it is also possible to use reagents such as sulfuric acid, hydrochloric acid, potassium hydroxide, sodium hydroxide, sodium carbonate, and ammonium hydroxide. The following examples are provided to illustrate the invention and should not be interpreted as limiting it in any way. Unless stated otherwise, all parts and percentages are by weight. Example 1 - Flotation of Iron Oxide Ore A series 600-g samples of iron oxide ore from Michigan were prepared. The ore contained primarily magnetite with smaller amounts of hematite, martite and goethite mineral species. The raw feed from which the samples were prepared was ground to 82 percent minus 75 micrometers and contained 11.3 percent silica and -6.7 percent iron. Each 600-g sample was individually ground along with 400 g of deionized water in a rod mill at about 60 RPM for two minutes. The resulting pulp was transferred to an Agitair 3000 ml flotation cell outfitted with an automated paddle removal system. Water was added to properly fill the cell volume. The pH of the slurry was left at the natural slurry of the ore which was 6,5 prior to the addition of the alkanol amines of this invention. The alkanol amine, when used, was added and the slurry allowed to condition for one minute. This was followed by the addition of the collector, as identified in Table I, followed by an additional minute of conditioning. Next, an amount of a polyglycol ether frother equivalent to 5 g per ton of dry ore was added followed by another minute of conditioning. The float cell was agitated at 900 RPM and air was introduced at a rate of 9.0 liters per minute. Removal of the silica concentrate was performed for ten minutes. Samples of the silica concentrate and product tailings containing the iron were dried, weighed and pulverized for analysis. They were dissolved in acid, and the iron content determined by the use of a D.C. Plasma Spectrometer. Using the assay data, the fractional recoveries and grades were calculated using standard mass balance formulas. The amount and grade of the iron recovered in the tailings are shown in Table 1 below. The data in Table I above shows that the addition of the alkanol amines in the reverse flotation process of this invention results in greater amounts of iron being recovered in the tailings than in similar processes run in the absence of the alkanol amines. For example, comparing Run 2 with Runs 5-8 shows that the addition of small amounts of alkanol amines results in increased iron recovery along with an increase in grade of the iron recovery. This indicates that the addition of a small amount of alkanol amine enhances the effectiveness of the 3-nonyloxy-propanamine collector used in these runs to collect silica. Examination of other runs in these examples shows that different alkanol amines used with different amine collectors consistently results in enhanced separation of the silica gangue from the desired iron in the process of this invention. Example 2 - Reverse Flotation of Silica from Phosphate Ores A series of 750 g samples of apatite-containing phosphate ore iron Florida were prepared. The raw feed from which samples were drawn has a particle size of about 90 percent less than 350 micrometers and 15 percent less than 37 micrometers. It contained 26.8 percent SiO₂ and 18.7 percent P₂O₅. The raw feed was washed with a sulfuric acid wash to clean the particle surfaces of any organics that were present due to prior processing stages. Each sample was transferred to an Agitair 3000 ml flotation cell outfitted with an automated paddle removal system. Sufficient dilution water was added to properly fill the cell volume. The pH of the starting pulp was adjusted to 6.4 with 1.0N NH₄OH. The alkanol amine, when used was added, followed by one minute of conditioning. Next, the amine collector was added followed by an additional minute of conditioning. A methylisobutyl carbinol frother was added at 5 g per ton of dry ore. The float cell was agitated at 900 revolutions per minute and air was introduced at a rate of 9.0 liters per minute. Silica concentrate was removed for ten minutes. The product tailings containing the phosphorus and the concentrate containing the silica gangue were dried, weighed and pulverized for analysis. They were dissolved in acid and the phosphorus (P₂O₅) content is determined by a D.C. Plasma Spectrometer. Using the assay data, the recovery and grade of phosphorus (P₂O₅) in the tailings were calculated using standard mass balance formulas. The results are shown in Table II below. The data in Table II above demonstrates the effectiveness of the present invention in the separation of silica from phosphate ore. In each instance, the addition of a small amount of an alkanol amine increases the ability of the amine collector to remove a silica concentrate from the phosphate tailings leaving a higher recovery of comparable grade phosphorus.

Claims: A process for the separation of silica or siliceous gangue from mineral values by reverse froth flotation using an amine collector characterized in that said flotation is carried out using the amine collector in the presence of at least one alkanol amine corresponding to the formula (R) x NH (3-x) wherein x is from 1 to 3 and R is separately in each occurrence a C₁₋₆ hydroxyalkyl, added prior to addition of the amine collector. A process as claimed in Claim 1, wherein the material separated is a particulate iron oxide ore. A process as claimed in Claim 1, wherein the material separated is a particulate phosphate ore. A process as claimed in any one of the preceding claims, wherein the alkanol amine comprises one or more of ethanol amine, diethanol amine, triethanol amine, propanol amine, isopropanol amine, butanol amine, and isobutanol amine. A process as claimed in Claim 4, wherein the alkanol amine is ethanol amine. A process as claimed in Claim 4, wherein the alkanol amine is diethanol amine. A process as claimed in any one of the preceding claims, wherein the alkanol amine is present in an amount of 0.001 to 1.5 kg/metric ton dry solids. A process as claimed in Claim 7, wherein said amount is 0.01 to 0.10 kg/metric ton. A process as claimed in any one of the preceding claims, wherein the amine collector is added in stages separated by froth concentrate collection. A process as claimed in any one of the preceding claims, wherein the alkanol amine is added during grinding of the gangue and mineral values. The use to enhance the performance of an amine collector in reverse froth flotation separation of silica or siliceous gangue from mineral values of an alkanol amine corresponding to the formula (R) x NH (3-x) wherein x is from 1 to 3 and R is separately in each occurrence a C₁₋₆ hydroxyalkyl, added prior to addition of the amine collector. A use as claimed in Claim 11, wherein the alkanol amine is as defined in any one of Claims 4 to 6.

Inventors: KLIMPEL RICHARD R, KLIMPEL, RICHARD R.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1991
Main classification: B03D1
IPC codes: B03D1