Abstract:
In the manufacture of printed circuit boards (PCBs), electroless nickel immersion gold (ENIG) plating is widely applied. During the plating process, excess nickel and gold plating solutions, which adheres to the workpiece, is removed. As a result, economical quantities of nickel and gold ions accumulate in the rinse water baths and can then be collected.
In this work, the simultaneously selective extraction and recovery of nickel and gold ions using a single-step operation of hollow fiber supported liquid membrane (HFSLM) technique was studied. Real rinse wastewater from the plating process containing trace nickel ions (Ni(II)) of 15 mg/L and gold ions (Au(I)) of 25 mg/L at initial pH value of 8.6±0.05 was used as feed solution. The influence of operating conditions: types of extractant and strippant at different concentrations, pH of stripping solution as well as types of diluents were also examined. Results demonstrate that the HFSLM system, using the liquid membrane phase consisting of synergistic binary organophosphorus extractants viz. 0.25 mol/L D2EHPA and 0.25 mol/L TBP dissolved in kerosene diluent, 0.50 mol/L HCl as stripping solution, and 200 mL/min flow rate for both feed and stripping solutions operating via recycling mode and countercurrently flow, can achieve the optimum selective separation efficiency of Ni(II) ions with 85.7% extraction and 83.2% stripping . Extraction of Ni(II) ions can rapidly reach 80% within 28 min. In contrast, percentages of extraction and stripping of Au(I) ions attained 15.6 and 1.94%, respectively.
Furthermore, various types of vegetable oil (palm, sunflower, soybean, coconut and rice bran) were investigated as diluents in the liquid membrane phase being more eco-friendly than kerosene diluent. Thus, it was found that all vegetable oil-based diluents can provide the separation efficiency close to kerosene. In addition, the developed mathematical model regarding mass transfer for predicting the concentration of Ni(II) ions in both feed and stripping solutions, was found to be of high accuracy and in good agreement with the obtained experimental data. This research paves the way towards reusing valuable metals for cost reduction and sustainable wastewater management.
