NICKEL HYDROXIDE RECOVERY FROM STAINLESS STEEL PICKLING LIQUOR BY SELECTIVE PRECIPITATION METHOD

Abstract

Nickel removal from the pickling liquor is done by several methods, in that selective precipitation method is the new process. Before , pickling is done by hydrochloric acid and sulfuric acids but now pickling process carried out with concentrated hydrofluoric and nitric acid because of less waste and pollution forming. The treatment of stainless steel pickling waste is compulsory due to its toxicity and polluting character. Moreover, metals and acids recovery is interesting from an economical point of view. Spent pickling liquor classical disposal consists of high-pH neutralization with lime and potassium or sodium hydroxide. This process generates high wastes volume and valuable materials lost, so recovery processes have been developed. Free acid recovery processes do not regenerate HF or HNO3 from metallic complexes in solution. However, acid retardation is the most implanted technique due to its low cost, although wastes volume is still high. Selective precipitation method has several advantages than any other metal removing process because of it's high purity product formation and the excellent efficiency in the metal recovery. In selective precipitation method initially we are removing the chromium and Iron as filtercake.So that the effluents contains very pure nickel and it may remove by adding alkali .The main parameters influencing the nickel hydroxide precipitation are temperature,pH, alkali concentration. Based on this parameters nickel hydroxide concentration will vary. The metal hydroxide ageing time influence on its solubility and the eventual reasons of such influence are of particular interest. Recent investigations were conducted with nickel hydroxide precipitate. Its solubility in neutral water is highly dependent on a solution pH . Several experiments are carried out with the different nickel and other metal concentrations with the alkali solutions and the purity of effluents after filtrations were studied. Parameters are changed and concentrate on the nickel recovery and it's purity.Optimum conditions were reached from different experimental results.