| Today, people pay attention more and more to the environment problem and sustainable development of economy, environment and society, since ecosystem has been deteriorated and resources has become depletive. Electroless nickel (EN) plating process has special advantages and can be widely applied to many fields. But when electroless nickel plating solution becomes spent, there are a lot of residual nickel (2000~7000mg/L) and phosphorus (80000~200000mg/L). It has been reported that heavy metal nickel can result in cancer and allergy, such as skin cancer, lung cancer, nose cancer and so on. The soluble nickel compound can also poison the organisms. So nickel and its compounds have been list in "Black list of pollution substance for preferential control in water". But at the same time, nickel is one kind of valuable metal resources. It is common knowledge that phosphorus is the limiting factor, which result in water eutrofication. It is obvious that if the spent EN plating baths is discharged without being treated, it will pollute the environment seriously.So it is significant to treat the spent EN baths effectively and recover its useful resources.In view of protecting environment and saving resources, we hope to choose suitable methods to treat spent EN plating baths for reducing environmental pollution and ecosystem destruction and recovering nickel and phosphorus resources.After recovering nickel by electrolysis and chemical reduction, purifying the residual nickel by Chemical precipitation method, treating and recovering phosphorus by precipitation and oxidation, the main conclusions of experiments were showed as follows:1. Recovering nickel by electrolysis is the process that nickel is reduced on the cathode with insoluble anode in the electrolysis system. The paper found that with Ti-Ru net as anode and foam nickel as cathode, the factors influencing the electrolysis process were pH value, electric intensity, temperature, nickel concentration and reaction time. When temperature being 80 C , pH=7~8, 1=0.45-0.5A, reaction time being 2 hours, residual nickel concentration in the spent baths could be reduced from 2018mg/L to 53.7mg/L and the removing rate was 97.3%, the electric current efficiency was 22.4%.2. According to condition experiment and orthogonal test of chemical reduction reaction, it was found that the dose of NaBH4 was the most important factor, then the pH value and temperature. When the reaction condition was of pH=6, 50C,10 min, 6ml NaBH4, therecovery rate of nickel from spent baths could reach to 99.85%. The residual nickel concentration was 10 mg/L.3. Chemical precipitation method with lime as precipitant was used to treat the residual nickel after recovering most of the nickel from the spent baths by electrolysis. For the first time in engineering, the quadratic regression orthogonal rotation design was chosen to design experiment. The relationship model between influence factors and residual nickel was made. The model could forecast the treatment very well. So it was helpful for us to choose the suitable test combination. It was also proven by experiment that the residual nickel could be reduced to Img/L in the optimal test combination scope.4. Ca(ClO)2 as precipitant and oxidizer was used to purify and recover phosphorus from the spent baths. When the condition was of pH=9.0, 80C , P: Ca(CLO)2=l:5.2, continuous stirring for 5 hours, the residual phosphorus concentration could be reduced below 2mg/L, which meets the need of discharge standard. For the residual nickel in the sediment was little, the precipitation could be considered of phosphate fertilizer.5. On the basis of experiments above, the process flow for treating spent EN plating baths was designed which was available on level of both economy and technology. The total cost for it was 23 RMB?per cubic meter.It was concluded that the synthetic treatment was one of the most effective way to purify and recover nickel and phosphorus from spent EN plating baths. It can save re...
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