Supported liquid membrane process for nickel removal from electroplating wastewater

Abstract

Supported liquid membrane (SLM) is one of the potential separation methods in treating wastewater loaded with toxic heavy metal ions owing to several advantages including simultaneous extraction and recovery processes, high separation factor, simple operation and it is easy to scale up. Right formulation, high stability and sustainable predominantly influence the success of the SLM process. Petroleum based diluents are hazardous whereas the single carrier is unable to efficiently extract nickel ion at lower pH. Liquid membrane loss leads to the SLM instability and short lifetime. In this study, a sustainable and stable SLM process using a mixture of carrier and cooking palm oil impregnated in composite membrane support was developed for the extraction and recovery of nickel ion from the electroplating wastewater. Electroplating wastewater was analyzed and SLM components such as carriers (di (2- ethylhexyl) phosphoric acid (D2EHPA), diisooctylthiophosphinic acid (Cyanex 302), tridodecylamine (TDA) and octanol), synergist carriers (Cyanex 302, TDA and octanol), diluents (kerosene and cooking palm oil) and stripping agents (sulfuric acid, hydrochloric acid and nitric acid) for nickel ion extraction were formulated via liquidliquid extraction process. The formulated liquid membrane containing D2EHPA and octanol in kerosene was impregnated in the membrane support pores of polyvinylidene fluoride (PVDF) with the features of 125µm thickness, 75% porosity and 0.22µm pore size. Parameters affecting SLM extraction of nickel such as carrier, synergist carrier and stripping agent concentrations as well as flow rate of feed and stripping phases were screened and optimized using the response surface methodology method. Several compositions of kerosene and cooking palm oil were studied to determine the feasibility of cooking palm oil in the extraction of nickel in SLM. The stability of SLM was investigated by developing a composite membrane support containing sulfonated poly (ether ether ketone) (SPEEK) and PVDF. Results showed that D2EHPA, octanol, cooking palm oil and sulfuric acid have potential as a carrier, synergist carrier, diluent and stripping agent, respectively. About 90 and 95% of nickel ions were successfully extracted and recovered, respectively under optimized conditions of 1.25M D2EHPA, 15% (v/v) octanol and 1.75M sulfuric acid. Upon applying 100% cooking palm oil as diluent, around 91% of nickel ions were extracted and 65% were recovered. The developed composite membrane support (SPEEK-PVDF) is capable of improving the SLM stability by reducing the liquid membrane loss from 47 to 23% upon applying the SPEEK layer at the feed side of the PVDF membrane support. High permeability (9.26 x 10-4 cms-1) and flux (6.48 x 10-7 molcm-2s-1) of nickel were achieved as the thickness of SPEEK was increased from 0.025 to 0.055mm. Recycling of the composite membrane support was found to be satisfactory until the ninth cycles with low weight loss percentage of the impregnated composite membrane support (8%). The findings of this study revealed that a sustainable and stable SLM process was successfully developed for the removal and recovery of nickel ion from the electroplating wastewater.