Research On Wet-processing Coupled With Foam Fractionation For The Metal From Waste Printed Circuit Board

Hydrometallurgy is a normal method for recovering metals from waste printed circuit boards(WPCB),but its leach solution has high processing cost and high pollution.Foam fractionation is a promising and green separation method,which can concentrate metal ions from their aqueous solution.Enrichment ratio was a more important parameter used to evaluate the performance of foam fractionation and it represents the concentration efficiency of this technique.This work was to achieve a high enrichment ratio of the desired metal ion through strengthening foam drainage using internal components.A novel foam fractionation column was developed by constructing internal components of vertical sieve tray internal peaked cap(VSTC)in the foam phase.In order to recover copper and gold in WPCB,the foam drainage efficiency of this internal component and its influence on foam fractionation performance were studied.Using sodium dodecyl sulfate(SDS)as the froth,the effects of the type,number of stages and the number of open cells around the VSTC on the foam drainage behaviour were investigated.Experimental results indicated that the drainage efficiency of the column with vertical sieve tray internal with horizontal cap and inclined cap(VSTCs)was significantly higher than those of other columns.The structural parameters of the VSTCs were determined.The number of plate stages was 5 and the number of open cells was 16.For recovering copper(Cu),WPCB was first treated by acid hydrolysis.the foam fractionation column with VSTCs internal components was used to recover Cu ions from the leaching liquor.A high leaching rate of Cu ions of 97.6% was obtained at the conditions of temperature40 °C,nitric acid concentration 6 mol/L,and leaching period 60 min.The drainage efficiency of VSTCs internal component was evaluated.Under the conditions of p H 4.0,gas volume flow rate 70 m L/min,SDS concentration 0.12 g/L and loading volume 500 m L,the enrichment ratio and recovery percnetage of Cu ions were 29.1 and 90.2%,respectively.Twostep reduction method was used to reduce Cu ions in the foamate.The results of XRD and SEM suggested that the collected Cu powder had good purity and crystallinity.In order to recover gold(Au)in WPCB,biological leaching was first performed,and the leaching liquor was used as the feeding solution of continuous foam fractionation.The experimental column was constructed with VSTCs internal components..The co-cultivation of Pseudomonas and Bacillus could shorten leaching period through providing a high cyanide concentration.Response surface methodology was used to optimize the biological leaching conditions of Au in WPCB.Under the optimum conditions of p H 10.0,feed liquid concentration 5 g/L and leaching period 34 h,the leaching rate of Au was 83.59%.After removing solid particles and cell biomass,the Au concentration in the leaching liquor was as high as 1.34 mg/L.Using cetyltrimethylammonium bromide(CTAB)as the collector,the drainage efficiency of foam fractionation column with VSTCS internal components was investigated,and the suitable number of stages of VSTCs was 5.Under the conditions of CTAB concentration 0.2 g/L,gas volume flow rate 100 m L/min,and feed flow rate 10 m L/min,the enrichment ratio and recovery percentage of Au ions were 43.6 and 87.4%,respectively.In summary,the foam fractionation column with VSTCs internal components could effectively strengthen foam drainage and improve the performance of foam fractionation.It was significant to facilitate the industrialization of foam fractionation through developing columns with satisfactory functionalities.