(376y) Separation of Zinc and Nickel from Industrial Wastewater through Supported Liquid Membrane Using Environmentally Benign Solvent

Effectiveness of supported liquid membrane (SLM) process for separation of Zn (II) and Ni (II) has been studied in this work. Nowadays SLM has received increased attention towards separation of heavy metals such as Hg, Pb, Cd, As, Zn and Ni etc.[1-3]. SLM technology has great potential as an alternative for separation of heavy metal as opposed to reverse osmosis, chromatography, adsorption, ion exchange, solvent extraction etc. The effluents emanating from various industries such as metal plating, electroplating, battery etc. are the main source of zinc related pollution whereas nickel is found in wastewater released from industries such as electroplating, battery, rubber processing, mining etc. Zn (II) and Ni (II) above concentrations 3 ppm and 0.02 ppm, respectively lead to environmental pollution. Traditionally the solvents used in the SLM are organic in nature which are inflammable and toxic to environment as well as to human health. Nevertheless the solvent used in this study, viz. sunflower oil, is environmentally as well as physiologically benign in nature. Addition of an extractant (a.k.a carrier agent) into the solvent seldom enhances efficiency of extraction and recovery of solute(s). Various extractants, such as tri-n-octylamine (abbreviated as TOA), di-(2-ethylhexyl) phosphoric acid (abbreviated as D2EHPA) and n-methyl-n,n,n-trioctylammonium chloride (a.k.a Aliquat 336), were employed in order to choose the best extractant for the SLM. D2EHPA has been found to be the best carrier agent for transport of Zn (II) whereas TOA is the best choice in favour of Ni (II) for the same purpose. The combination of solvent and carrier is termed as membrane phase. Both the membrane phases in this study, viz. “D2EHPA-sunflower oil” for Zn (II) and “TOA-sunflower oil” for Ni (II), are environmentally and physiologically “green” in nature. The polymeric support of SLM is made of polyvinylidene fluoride (or abbreviated as PVDF) with pore size of 0.22 µm. Among various strippants employed in this study for recovery of Zn ion, such as sulphuric acid (H₂SO₄ leading to 33.32% recovery of zinc and 35.46% recovery of nickel), ammonium chloride (NH₄Cl leading to 23.58% recovery of zinc and 21.87% recovery of nickel), sodium chloride (NaCl leading to 10.07% recovery of zinc and 11.96% recovery of nickel) and ethylene di-amine (C₂H₄(NH₂)₂ leading to 6.20% recovery of zinc and 7.52% recovery of nickel), it has been observed that H₂SO₄ is the best stripping agent. The performance of SLM in transport of solute(s) has been optimized by tuning various parameters, viz. concentration of solute in source phase (effluent), pH of source phase, concentration of strippant in stripping phase, concentration of carrier in the membrane phase, stirring speed and run time. It has been observed that the optimum concentration of Zn (II) and Ni (II) in source effluent should be 100 mg L^-1 (for both solutes) in order to achieve best transport performance while the studied range in this category was 50 to 400 mg L^-1. Further 3% (vol/vol) D2EHPA in the membrane phase, within studied range of 0 to 5%, was ideal for transportation of Zn (II) whereas 5% (vol/vol) TOA was ideal for transportation of Ni (II) within the studied range 0 to 8%. Similarly 0.1 M H₂SO₄ in stripping phase (with studied range of 0.01 to 1 M), pH 5 in source phase (with studied range 2 to 8), 120 rpm of stirring speed in source and stripping phase (with studied range 60 to 250 rpm), 48 hours of run time (with studied range of 24 to 72 hrs) have been found to be most suitable for transport of Zn (II) in the most efficient manner. On the other hand 0.1 M H₂SO₄ in stripping phase (with studied range of 0.01 to 1 M), pH 4 in source phase (with studied range 2 to 8), 120 rpm of stirring speed in source and stripping phase (with studied range 60 to 250 rpm), 48 hours of run time (with studied range of 24 to 48 hrs) have been found to be most suitable for transport of Ni (II) in the most efficient manner. The efficiencies of extraction and recovery with the aforementioned optimized operating conditions are 42% and 53%, respectively for Zn (II) whereas the same for Ni (II) are 45% and 53%, respectively. Combinatorial transport of both Zn (II) and Ni (II) in a single SLM setup is being investigated at present. The results of SLM process can further be used for the separation of solute(s) through hollow fibre membrane (HFM).

References:

[1] E. Jean, D. Villemin, M. Hlaibi, L. Lebrun, Heavy metal ions extraction using new supported liquid membranes containing ionic liquid as carrier, Sep. Purif. Technol. 201 (2018) 1–9.

[2] B. Swain, K. Sarangi, R. P. Das, Effect of different anions on separation of cadmium and zinc by supported liquid membrane using TOPS-99 as mobile carrier, J. Membr. Sci. 277 (2006) 240–248.

[3] P.K. Parhi, K. Sarangi, Separation of copper, zinc, cobalt and nickel ions by supported liquid membrane technique using LIX 84I, TOPS-99 and Cyanex, Sep. Purif. Technol. 59 (2008) 169–174.