Treatmental Processes For Spent Electroless Nickel Plating Baths

With the development of electroless nickel plating technology, theenvironmental problem has become more and more serious. The nickel in thewaste electroless nickel plating baths is not only a carcinogen, but also onekind of expensive metal. The direct discharge of this kind of wastewater isharmful to the environment and human health, and leads to resource-wasting.It is necessary to select suitable treatment processes in order to carry outdirect discharge.The present thesis concerned of environmental protection and economy,combining with the characteristics of the spent electroless nickel plating bath.At the same time, some methods for the treatment and recovery of nickel fromthe spent electroless nickel plating bath were discussed, such as reduction,adsorption and precipitation processes. In addition, the technology of recoveryphosphorus was also investigated. The electroless nickel plating bath wasprocessed through sodium borohydridet reduction, kaolin adsorption andchemical precipitation respectively, and the research results were given asfollows:(1) Using the reduction method of sodium borohydride reagent, the nickelion concentration in the electroless nickel plating bath was reduced greatly.The orthogonal experiment results showed that the optimum experimentalconditions were as follows: pH5, temperature40℃, sodium borohydridedosing quantity3.5g/L. And the removal rate of nickel ions could reach to94.2%under the optimal conditions.(2) Kaolin adsorption method was also selected to remove nickel fromelectroless nickel plating bath, and the optimum technological conditions wereas follows: kaolin concnetration70g/L, adsorption time80min, pH6. And theremoval rate of nickel ions could reach to89.1%under the optimal conditions.(3) Combination of oxidation broken complexing and chemicalprecipitation processing was a very effective method to reduce nickel ionconcentration in the waste water. The Orthogonal experimental results showedthe optimal conditions: hydrogen peroxide30mL/L, sodium hydroxide15.67g/L, and reaction temperature80℃. The removal rate of nickel is close to 100%under the optimal condittions, and the concentration of residual nickelions is only0.89mg/L.(4) Comparison of three kinds of processingCompared with the reduction method, adsorption and precipitation, it wasfound that the combining method of oxidation broken complexing withchemical precipitation was the best process to treat the spent electroless nickelplating bath, which could take up the economic and environmental benefitsdramaticly.(5) Treatment of phosphorusCalcium chloride is a kind of effective precipitation agent, which can beused to deal with the phosphorus in the spent electroless nickel plating bath,and the sediment can be used as phosphatic fertilizer. The results showed thatthe total phosphorus removal rate was up to99.99%and the total phosphoruscontent of residual was0.83mg/L when calcium chloride dosing quantity was70g/L, reaction time3h, pH8.0.After the removal processes of nickel and phosphorus mentioned above,the spent electroless nickel plating bath could be discharged directly accordingto the national discharge standard “Discharge Standards for ElectroplatingPollutants”(GB21900-2008).