Method of recycling electroless nickel waste
View Patent ↗An electroless nickel plating bath is provided that utilizes hypophosphite ions as a reducing agent and is substantially free of sulphate and sodium ions. Spent nickel in the plating bath is removed using an ion exchange resin and the remaining effluent solution is usable for manufacturing fertilizer compositions. The nickel is processed for inclusion back into the plating bath. Thus, the process of the invention allows for the indefinite use of the solutions without discharging hazardous waste.
1. A method of operating and regenerating an electroless nickel plating bath, the method comprising the steps of:
a) depositing electroless nickel from the electroless nickel plating bath onto a substrate, wherein the electroless nickel plating bath comprises a source of nickel ions and a source of hypophosphite ions;
b) maintaining a concentration of nickel ions and hypophosphite ions in the plating bath such that plating can continue;
c) operating the plating bath until a desired number of metal turnovers is reached;
d) processing a portion of the electroless nickel plating bath through a cation exchange resin to separate nickel, wherein after the nickel is removed, a phosphite solution comprising ammonium phosphite, ammonium hypophosphite, and organic acid remains and wherein the phosphite solution comprises less than 10 g/l of sodium ions and less than 10 g/l of sulfate ions;
e) regenerating the cation exchange resin with hypophosphorous acid thereby creating a dilute nickel hypophosphorous acid solution;
f) increasing the concentration of nickel in the dilute nickel hypophosphorous acid solution of step e) by adding a source of nickel ions selected from the group consisting of nickel carbonate, nickel hydroxide, nickel oxide, and combinations thereof to the solution to form a concentrated nickel solution; and
g) adding the concentrated nickel solution of step f) to the plating bath of step b) to maintain the concentration of nickel ions in the plating bath.
2. The method according to claim 1 , wherein the concentration of nickel in the phosphite solution after processing through the cation exchange resin is less than about 5 mg/l.
3. The method according to claim 2 , comprising the step of removing additional nickel ions from the phosphite solution by treating the phosphite solution with dimethyldithiocarbamate or diethyldithiocarbamate ions.
4. The method according to claim 2 , further comprising the step of concentrating the phosphite solution using evaporation or reverse osmosis.
5. The method according to claim 4 , wherein the phosphite solution is usable as a liquid fertilizer composition.
6. The method according to claim 1 , wherein the source of nickel in the electroless nickel plating bath is nickel carbonate.
7. The method according to claim 1 , wherein the plating bath further comprises acetic acid, lactic acid, or a combination thereof.
8. The method according to claim 1 , wherein the plating bath further comprises a source of lead ions, a source of iodate ions, or a combination thereof.
9. The method according to claim 1 , wherein the pH of the electroless nickel bath is about 4.0 to 6.0.
10. The method according to claim 9 , wherein the pH of the electroless nickel bath is adjusted by adding a pH adjuster selected from the group consisting of ammonia, potassium carbonate, potassium hydroxide and combinations thereof.
11. The method according to claim 1 , wherein during step d) the pH of the solution is above about 4.
12. The method according to claim 1 , wherein the nickel plating bath is processed through at least four turnovers in step c).