Method of treating liquid wastes containing heavy metal chelate compounds

Abstract: A method of treating liquid wastes containing heavy metal chelate compounds which comprises reducing the pH of liquid wastes containing the heavy metal chelate compounds to 4 or less, adding iron polysulfate or at least one heavy metal ions selected from a source of Fe⁺⁺, Fe⁺⁺⁺, Cu⁺⁺, Ni⁺⁺ and Zn⁺⁺ other than the iron polysulfate to form an iron chelate com­ pound, then forming a solution containing Ca⁺⁺ ions at pH 9 or more, and flocculating to precipitate thereby separating the re­ sulted heavy metal hydroxides. The method gives a high heavy metal and COD removal rates, as well as showing good separatability for flocks upon flocculating treatment.

Description: BACKGROUND OF THE INVENTION This invention relates to a method of treating liquid wastes containing heavy metal chelate compounds. Since liquid wastes discharged from plants for manufacturing printed circuit boards or the likes contain heavy metal chelates such as Cu-EDTA derived from chemical copper plating solutions, if the liquid wastes are discharged as they are into river or like other water bodies, they may cause circumstantial pollutions. Various methods of treating these liquid wastes have hitherto been put to practical use. For example, there have been known relatively effective treating methods such as an excess calcium hydroxide addition method of adding calcium hydroxide to liquid wastes containing Cu-EDTA chelates to adjust pH to 12 or more and then adding a flocculant thereby causing flocculating precipitation, an oxidative separation method of treating Cu-EDTA by using a powerful oxidizer and an adsorption method of treating Cu-EDTA by means of ion exchange resins or the likes. Heavy metals in the liquid wastes can be removed more or less by these treating methods. However, the excess calcium hydroxide addition method requires a much chemical cost and, in addition, causes scalings to pumps and pipeways and cloggings in the filter. The oxidative decomposition method requires a longer processing time to attain a sufficient removal rate even when the solution is warmed. The adsorption method requires a high regeneration of ion exchange resins or the likes and no effective improvement can be expected for the Cu-removal rate (refer to Patent KOKOKU (Post-Exam Pubin) No. 25280/1982). SUMMARY OF THE INVENTION The object of this invention is to provide a method of treating liquid wastes containing heavy metal chelate compounds giving a high heavy metal and COD removal rates, as well as showing good separatability for flocks upon flocculating treatment. BRIEF DESCRIPTION OF THE DRAWINGS The drawing is a flow chart of one embodiment for carrying out this invention, wherein are shown a liquid wastes store tank 1, a first treating tank 2, a second treating tank 3, a thickener 4, a dehydrator 5 and pumps P1 - P3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The foregoing object of this invention can be attained by a method of treating aqueous plant waste containing copper chelate compounds and cheating agents which comprises adding calcium and heavy metal ions to said waste, characterized by the following steps, (a) reducing the pH of said waste to 4 or less, preferably between 2-4 and most preferably between 2-3. (b) simultaneously or successively adding heavy metal ions selected from at least a source of Fe²⁺, Fe³⁺, Cu²⁺, Ni²⁺ and Zn²⁺ ions, wherein said heavy metals are added in an amount to provide an equivalent ratio of heavy metal ions to chelating agent in said waste of from 4:1 to 10:1, (c) adjusting the pH of the treated waste by adding Ca²⁺ ions to provide a pH, preferably from 9 to 10, (d) adding a flocculant to precipitate heavy metal hydroxides, and (e) separating said metal hydroxides to obtain the treated aqueous waste. The iron ions source can be iron polysulfate having the general formula [Fe(OH) n (SO₄) (3-n)/2 ] m , wherein n is below 2 and m is over 10. The iron polysulfate represented by the above formula: [Fe(OH) n (SO₄) (3-n)/2) ] m (where n < 2, m > 10) is manufactured and sold from Nittetsu Kogyo K.K. and has the composition, for example as shown in Table 1. Item Concentration Fe⁺⁺⁺ 160.6 g/l Fe⁺⁺ 0.84 g/l SO₄ ⁻⁻ 377.0 g/l Cd less than 0.01 mg/l Pb 1.40 g/l Hg less than 0.005 mg/l As less than 0.01 mg/l Specific gravity 1.464 Further, Fe⁺⁺, Fe⁺⁺⁺, Cu⁺⁺, Ni⁺⁺, Zn⁺⁺, are available, for example, from a solution and a solid of ferrous sulfate, ferric sulfate, ferrous chloride, ferric chloride, copper sulfate, nickel sulfate, nickel chloride, and zinc chloride, and sludges containing the above-mentioned heavy metal ions and calcium ions. The amount of these compounds added is from 4 to 10 times, as converted into metal, as large as all chelating equivalents contained in chemical copper plating waste solutions containing copper chelates compounds and chelating agents. Ca⁺⁺ ions are supplied by dissolving one selected from the group consisting of Ca(OH)₂, CaO and CaCO₃, the pH of which is adjusted to 9 or more. Further, NaOH, Na₂CO₃ and MgO may also be used together. If the pH value is less than 9, chelates of heavy metals other than copper may remain or copper chelate are formed again to reduce the heavy metal and COD removal rates. For adjusting pH to 4 or less, while sulfuric acid is usually employed, hydrochloric acid may also be used. If pH is greater than 4, heavy metal chelates may remain and no desirable precipitations can be separated even with the addition of the flocculant to reduce the heavy metal removal rate. As the flocculant, while polyacrylamide type anionic polymeric flocculants are preferred, cationic or nonionic polymeric flocculants may also be used. Further, inorganic flocculant such as polyaluminum chloride may be used as well. The amount of the flocculant added is from 0.5 to 10 ppm and, preferably, from 1 to 2 ppm. Usually, the flocculant is added in the form of an aqueous 0.05 - 0.2% solution after the addition. Then, liquid wastes are stirred, left for about 2 - 10 minutes and concentrated by a thickener or the like from which slurries are separated to remove by an Oliver type vacuum dehydrator or the like. The polyacrylic amide type anionic polymeric flocculant is available, for example, as EDP-351 manufactured by Kurita Kogyo K.K. It has molecular weight of 900 x 10⁴, bulk specific gravity of 0.75, effective pH range from 7 to 12 and pH value in an 0.1% aqueous solution of 8.3. The cationic polymeric flocculant can include Himolock MP-473H, Himolock MP-473L manufactured by Kyoritsu Yuki Kagaku Kogyo Institute. This invention will now be described more specifically referring to examples. Example 1 To 10 m³ of chemical copper liquid wastes discharged from a printed circuit board manufacturing plant (containing 15 ppm Cu, 165 ppm EDTA and 80 ppm COD), a 5% sulfuric acid solution was added to adjust pH of the solution to 2.5. Then, 60 ppm (as converted into iron) of iron polysulfate (POLYTETSU, 11% ferric content: manufactured by Nittetsu Kogyo) was added to and mixed with the solution. After stirring for 3 minutes, 10% calcium hydroxide was added to adjust pH to 10. Further, an anionic polyacrylic amide flocculant (KURIFLOCK EDP351: manufactured by Kurita Kogyo) was added in an amount of 1 ppm to the solution. After leaving for 5 minutes, precipitated slurry-like solids were separated by an Oliver type vacuum dehydrator. The contents for copper and iron in the resultant supernatant were determined to obtain the results as shown in Table 2. Cu Fe COD Content (ppm) 0.22 less than 0.01 12 Removal rate (%) 98.5 100 85 Example 2 The same procedures as in Example 1 were repeated except for varying the concentration of the chemical copper liquid wastes and the addition amount of the iron polysulfate in the first treating step, and the pH value in the second treating step as shown in Table 3. The contents for copper and iron in the treated water were determined to obtain the results as shown in Table 3. Concentration of chemical copper liquid wastes (ppm) Concentration iron polysulfate (ppm) PH Heavy metal concentration in treated water Cu EDTA Cu Fe 30 70 100 10 0.56 0.56 11 0.56 0.28 11.5 0.56 ND 12 0.56 ND 200 10 0.56 0.28 11 0.23 ND 11.5 0.23 ND 12 0.33 ND Example 3 The same procedures as in Example 1 were repeated except for varying the concentration of the chemical copper liquid wastes (Cu: 3,000 ppm, EDTA: 35,000 ppm, COD: 18,000 ppm) to 200 liter, the addition amount of the iron polysulfate to 45,000 ppm and the addition amount of the flocculant to 50 ppm. The contents for copper and iron in the treated water were determined to obtain the results as shown in Table 4. Cu Fe COD Content (ppm) 7.3 5.5 680 Removal rate (%) 99.8 100 96.2 Comparative Example 1 The procedures in Example 1 were repeated without adding the iron polysulfate in the first treating step. The copper content in the solution was 10 ppm. In addition, the precipitating property of the flocks was poor in this treatment after the addition of the flocculant. Comparative Example 2 Iron polysulfate was added to the chemical copper liquid wastes with the solution pH as it was not reduced to 2.5 in the first treating step and pH was adjusted to 10 in the second treatment step in the same manner as in Example 1. The copper content was 10 ppm and the iron content was 25 ppm in the solution after the treatment. The color of the solution after adding the flocculant in this treatment was yellowish blue. Example 4 To 10 m³ of chemical copper liquid wastes discharged from a printed circuit board manufacturing plant (Cu: 15 ppm, EDTA: 165 ppm, COD: 142 ppm), 5% sulfuric acid solution was added to adjust pH to 2.5. Then, 0.5 m³ sludges, 5% to the liquid wastes water (water content: 98%, Cu: 1240 ppm, Fe: 620 ppm, Ca: 15,000 ppm) was added and mixed to adjust pH to 2.5 again. After stirring for 3 minutes, 10% calcium hydroxide was added to adjust pH to 10. Further, an anionic polyacrylic amide flocculant (KURIFLOCK EDP351: manufactured by Kurita Kogyo) was added in an amount of 2 ppm to the solution. After leaving for 5 minutes precipitated slurry-like solids were separated by an Oliver type vacuum dehydrator. The contents for copper and iron in the obtained supernatant were determined to obtain the results as shown in Table 5. Cu Fe COD Content (ppm) 0.33 less than 0.01 28 Removal rate (%) 97.8 - 80.3 Example 5 The same procedures as in Example 4 were repeated except for varying the sludges used in the first treatment step (water content 98%, Cu: 370 ppm, Fe: 280 ppm, Ni: 60 ppm, Zn: 160 ppm, Cr: 15 ppm, Ca: 14,000 ppm) from those shown in Table 5. The contents for copper, nickel and COD in the supernatant obtained in this treatment were determined to obtain the results as shown in Table 6. Cu Ni COD Content (ppm) 0.26 0.11 12 Removal rate (%) 98.3 - 75.4 Example 6 The same procedures as in Example 4 were repeated except for using 2 ppm of the flocculant in the second treatment step and adding 2% (0.2 m³) of sludges together with the flocculant to the solution. The contents for copper, iron and COD in the supernatant obtained in this treatment were determined to obtain the result shown in Table 7. Cu Fe COD Content (ppm) 0.23 less than 0.01 13 Removal rate (%) 98.5 - 90.8 Comparative Example 3 The procedures in Example 4 were repeated without adding the sludges in the first treating step. The content was 10 ppm for copper and 107 ppm for COD in the solution. In addition, the precipitating property of the flocks was poor in this treatment after the addition of the flocculant. Comparative Example 4 Sludges were added to the chemical copper liquid wastes with the solution pH as it was not reduced to 2.5 in the first treating step and pH was adjusted to 10 in the second treatment step in the same manner as in Example 1. The content in the solution was 2.2 ppm for copper content, 0.5 ppm for iron and 650 ppm for COD. The removal rate was inferior to that in Example 4. Example 7 To 10 m³ of chemical copper liquid wastes discharged from a printed circuit board manufacturing plant (containing Cu: 15 ppm, EDTA: 165 ppm and COD: 142 ppm), sulfuric acid was added to adjust pH to 2.5. Then, ferrous sulfate (containing 10% ferrous content) was added and mixed with the solution so as to provide 200 ppm of Fe⁺⁺. After stirring for 3 minutes, 10% calcium hydroxide was added to adjust pH to 11. Further, an anionic polyacrylic amide flocculant (KURIFLOCK EDP351: manufactured by Kurita Kogyo) was added in an amount of 1 ppm to the solution. After leaving for 5 minutes, precipitated slurry-like solids were separated by an Oliver type vacuum dehydrator. The contents for copper, iron and COD in the obtained supernatant were determined to obtain the results as shown in Table 8. Cu Fe COD Content (ppm) 1.22 25.3 5.6 Removal rate (%) 91.8 - 60.6 Example 8 The same procedures as in Example 4 were repeated except for replacing the heavy metal-containing salts used in the first treatment step with a mixed solution of copper sulfate and nickel sulfate (Cu: 50 ppm, Ni: 50 ppm). The contents for copper, nickel and COD in the supernatant obtained in this treatment were determined to obtain the results as shown in Table 9. Cu Ni COD Content (ppm) 1.65 5.91 6.6 Removal rate (%) 89.0 - 53.4 Example 9 The same procedures as in Example 7 were repeated except for using 200 liter of chemical copper liquid wastes (Cu: 3,000 ppm, EDTA: 35,000 ppm and COD 28,500 ppm) and 100 liter of ferric chloride etching liquid wastes (Fe: 140,000 ppm, Cu: 50,000 ppm) and adding 50 ppm of the flocculant. The contents for copper, iron and COD in the supernatant of the treated water were determined to obtain the results as shown in Table 10. Cu Fe COD Content (ppm) 28 103 4,400 Removal rate (%) 99.1 - 84.6 Comparative Example 5 The same procedures as in Example 7, were repeated without adding heavy metal-containing salts in the first treatment step. The copper concentration in the supernantant was 6.5 ppm. Less flocks were formed in this treatment after the addition of the flocculant, and the precipitating property was poor. Comparative Example 6 The same procedures as in Example 7 were repeated except for adding heavy metal-containing salts to the chemical copper liquid wastes with the pH solution as it was not reducing to 2.5. The copper content in the supernatant was 4.1 ppm and the flock precipitating property was poor like that in Comparative Example 2. These examples are some embodiments of this invention and don't restrict the scope of the invention. According to the invention, it can be applied to treatment of liquid wastes containing other heavy metal such as, for example, nickel, zinc and cadmium, as well as liquid wastes containing copper chelate compounds. Furthermore, as cheating agents, polyaminocarboxylic acid such as DTPA, NTA, DTA or the like, and amine can be used.

Claims: A method of treating aqueous plant waste containing copper chelate compounds and chelating agents which comprises adding calcium and heavy metal ions to said waste. characterized by the following steps. (a) reducing the pH of said waste to 4 or less, (b) simultaneously or successively adding heavy metal ions selected from at least a source of Fe²⁺, Fe³⁺, Cu²⁺, Ni²⁺ and Zn²⁺ ions, wherein said heavy metals are added in an amount to provide an equivalent ratio of heavy metal ions to chelating agent in said waste of from 4:1 to 10:1, (c) adjusting the pH of the treated waste by adding Ca²⁺ ions to provide a pH from 10 to 12, (d) adding a flocculant to precipitate heavy metal hydroxides, and (e) separating said metal hydroxides to obtain the treated aqueous waste. The method of claim 1, wherein the iron ions source is iron polysulfate having the general formula [Fe-(OH) n (SO₄) 3-n)/2 ] m , wherein n is below 2 and m is over 10. The method of claim 1, wherein the sources of heavy metal ions are selected from ferrous sulfate, ferric sulfate, copper sulfate, nickel sulfate, nickel chloride and zinc chloride, and sludges containing the above-mentioned heavy metal ions and Ca²⁺ ions. The method of claim 1, wherein the flocculant is selected from anionic polymeric, cationic polymeric, nonionic and inorganic flocculants. The method of claim 1, wherein said flocculant is added in an amount from 0.5 to 10 ppm. The method of claim 4, wherein the anionic polymeric flocculant is a polyacrylic amide and the inorganic flocculant is polyaluminum chloride.

Inventors: KATOH SEIJI, KATOH, SEIJI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1985
Main classification: C02F1
IPC codes: C02F9, C02F1