Magnetic Separation of Nickel from Electroless Plating Waste Fluid using a HTS Bulk Magnet

Abstract

A magnetic separation experiment to recycle nickel from the waste fluid of electroless plating processes was conducted using the open-gradient magnetic separation technique and a HTS bulk magnet system. A magnetic pole containing Gd123-based bulk superconductors was activated to 3.44 T at 34.9 K using a 5 T superconducting solenoid and the field cooling method. The coarse precipitates of nickel sulfate are composed of phosphite ions, which are yielded during the plating reaction by controlling the temperature and pH. Next, the open-gradient magnetic separation technique was employed, with use of water channels to separate the nickel-sulfate crystals from the mixture of the nickel sulfate and phosphite compounds based on the difference in magnetic properties. From the concentrations of each precipitate attracted to the magnetic pole, we succeeded in collecting nickel-sulfate crystals preferentially to the phosphite ions soon after crystal growth began.