Separation of the Metals in the Spent Electroless Nickel Plating Baths by Solvent Extraction

摘要

With increasing importance of the electroless nickel plating technology in many fields such as electronic and automobile industries, the treatment of the spent baths is becoming a serious problem. Although the spent baths are currently treated by the conventional precipitation method, a method without sludge generation is desired. This work aims at establishing a recycling process of nickel from the spent baths. Solvent extraction of nickel, iron, and zinc in two types of spent baths (A and B) has been investigated using 2-hydroxy-5-nonylacetuphenune oxime (LIX84I) and the acidic organophosphorus compounds such as bis (2-ethylhexyl) phosphoric acid (D2EHPA), 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC88A) and bis (2, 4, 4-trimethylpentyl) phosphinic acid (Cyanex272) as the extractants. Spent bath A is weakly acidic (pH 4.8) and contains 70 g m~(-3) of zinc as an impurity, and spent bath B is very weakly acidic (pH 6.0) and contains boron. The following results have been obtained: (i) Nickel in spent bath A can be extracted with LIX84I at the pH larger than 6 with high efficiency leaving most of zinc and iron in the aqueous phase. Also, nickel in spent bath B can be efficiently extracted without adjusting pH. (ii) According to the McCabe-Thiele analysis, the concentrated nickel sulfate solution (>100kg-Ni m~(-3)) with low sulfuric acid content is obtained by the countercurrent two stage stripping from the Ni-bearing L1X841 using the mixed solution of 0.9 kmol m~(-3) NiSO_4 and 1 kmol m~(-3) H_2SO_4 as the stripping reagent. (iii) Iron and zinc in spent bath A can be selectively extracted with the acidic organophosphorus compounds. PC88A and Cyanex272 are more advantageous than D2EHPA because, in the former extractants, the coextraction of nickel is tower and the stripping of iron and zinc is easier. Based on these results, the flowsheets for recovering nickel from the spent baths are proposed.