Method of treating mine drainage

1. A method for inhibiting precipitation of calcium salt and metal oxide and/or metal hydroxide from hard mine drainage water comprising:

(a) providing hard mine drainage water having a pH of from 4.5 to 10; calcium hardness greater than 100 mg/l of Ca +2 as calcium carbonate; alkalinity greater than 100 mg/l as calcium carbonate; and one or more metal ions or metal salts selected from the group consisting of iron, copper, zinc, lead, mercury, cadmium, arsenic, barium, selenium, silver, chromium, aluminum, manganese, nickel, cobalt, uranium, and antimony; and

(b) adding a scale control agent to the mine drainage water, wherein the scale control agent is one or more selected from the group consisting of polymeric scale control agents, water-soluble polycarboxylates, phosphonates, organic phosphates, organic polyphosphates, and sulfonates, at a level sufficient to inhibit precipitation of calcium salt and metal oxide and/or metal hydroxide in said hard mine drainage water.

2. The method of claim 1 , further comprising the step of adding an oxidizing agent to the mine drainage water.

3. The method of claim 2 , wherein the oxidizing agent is one or more selected from the group consisting of peroxides, hypochlorites, permanganates, percarbonates, perborates, perchlorates, chromates, ozone, osmium tetroxide, sodium metaperiodate, nitric acid, nitrous acid, and persulfates.

4. The method of claim 3 , wherein the oxidizing agents are peroxides selected from hydrogen peroxide and calcium peroxide, and permanganates selected from sodium permanganate and potassium permanganate, wherein the peroxides and permanganates are applied sequentially or in combination to the mine drainage water.

5. The method of claim 2 , wherein the oxidizing agent is added to the drainage water at a level of 0.1 mg/l to 500 mg/l.

6. The method of claim 1 , further comprising the step of precipitating and settling the metals in their hydroxide form.

7. The method of claim 6 , further comprising the step of adding an alkalinity agent to raise the pH of the mine drainage water, prior to precipitating and settling the metals in their hydroxide form.

8. The method of claim 7 , wherein the alkalinity agent is one or more selected from the group consisting of caustic soda, soda ash, ammonia, and lime.

9. The method of claim 7 , wherein the alkalinity agent is lime.

10. The method of claim 6 , including the step of adding one or more of a coagulating agent and a flocculent to the drainage.

11. The method of claim 10 , wherein the coagulating agent is one or more selected from the group consisting of inorganic coagulants, organic coagulants, and inorganic/organic coagulant blends.

12. The method of claim 11 , wherein the inorganic coagulants are one or more selected from the group consisting of alum, aluminum chloride, polyaluminum chloride, aluminum chlorohydrate, ferric chloride, and ferric sulfate.

13. The method of claim 11 , wherein the organic coagulants are one or more selected from the group consisting of poly(diallyl dimethyl ammonium chloride), copolymers of diallyl dimethyl ammonium chloride, polyamines, and quaternized polyepichlorhydrins.

14. The method of claim 10 , wherein the coagulating agent is added to the drainage water at a level of from 0.1 to 100 mg/l.

15. The method of claim 10 , wherein the flocculent is one or more selected from the group consisting of polyethyleneoxides, non-ionic polyacrylamides, anionic polyacrylamides, cationic polyacrylamides, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, non-ionic starches, anionic starches, cationic starches, guar, and Irish moss.

16. The method of claim 10 , wherein the flocculant is added to the drainage water at a level of from 0.01 to 100 mg/l.

17. The method of claim 1 , wherein the scale control agent has low toxicity toward marine life.

18. The method of claim 1 , wherein the polymeric scale control agents are one or more selected from homopolymers and copolymers of one or more monomers selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, acrylamide, 2-acrylamide-methyl propane sulfonic acid, ethoxylated methacrylate, itaconic acid, polyethylene glycol monomethacrylate, t-butyl acrylamide, sodium styrene sulfonate, sodium vinyl sulfonate, hydroxy propyl acrylate, hydroxy propyl methacrylate, 3-allyloxy-2-hydroxy propane sulfonic acid, vinyl phosphonic acid and their corresponding salts.

19. The method of claim 1 , wherein the scale control agent is one or more selected from the group consisting of poly(acrylic acid), hydrolyzed poly(maleic anhydride), a copolymer comprising acrylic acid and 2-acrylamide-methyl propane sulfonic acid, sulfonated polyphosphino carboxylic acid, phosphonocarboxylic acid (sulfonated) copolymer, acrylic acid-sulfophenylmethallyl ether copolymer, maleric anhydride-ethyl acrylate-vinyl acetate copolymer, 2-phosphonobutane-1,2,4-tricarboxylic acid, 1-hydroxy ethylidene 1,1-diphosphonic acid, amino tri(methylene phosphonic acid), orthophosphate, polyphosphates, polyether polyamino methylene phosphonates, N,N-bis(phosphonomethyl)-2-amino-1-propanol and their corresponding salts.

20. The method of claim 1 , wherein the scale control agent is added to the water at a level of from 0.01 mg/l to 100 mg/l.

21. The method of claim 1 , wherein the mine drainage water has greater than 0.5 mg/l of one or more metal ions or metal salts selected from the group consisting of iron, copper, zinc, lead, mercury, cadmium, arsenic, barium, selenium, silver, chromium, aluminum, manganese, nickel, cobalt, uranium, and antimony.

22. The method of claim 1 , wherein the calcium salt is selected from the group consisting of calcium carbonate, calcium sulfate and mixtures thereof.

23. The method of claim 22 , wherein the calcium salt is calcium carbonate.

24. The method of claim 1 , wherein the metal oxide is iron oxide.

25. The method of claim 1 , wherein the metal hydroxide is iron hydroxide.