Effect of graphene oxide addition on the characteristics and performance of polymer inclusion membrane for gold extraction

The demand of gold production kept increasing gradually, forcing the industries to double the gold production. Conventionally, cyanide leaching method is the most active technique used by many industries for gold production. This method consists of two main stages known as the extraction stage where aurocyanide (Au (CN2)-) solution was formed and the recovery stage. The most crucial stage in gold production was the recovery stage since the extraction of gold as final product took place. In industry, recovery stage commonly applied either the carbon adsorption or the solvent extraction (SX) on extracting the gold from Au (CN2)- solution. However, carbon adsorption revealed slow in gold extraction while volatile organic compound (VOC) in the SX was harmful towards the environment. Indeed, employment of polymer inclusion membranes (PIMs) integration with graphene oxide (GO) was introduced as an alternative to replace the conventional methods in gold extraction. In this study, PIMs were fabricated with 50 wt% poly (vinylidene fluoride-co- hexafluoropropylene) (PVDF-co- HFP) as the base polymer, 40 wt% di-(2-ethylhexyl) phosphoric acid (D2EHPA) as the carrier, 10 wt% dioctylphthalate (DOP) as the plasticizer and altered GO composition with 0 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt% and 2.0 wt% as an additive labeled M1, M2, M3, M4 and M5, respectively. PIMs were characterized by their physico-chemical properties via Scanning Electron Microscope (SEM), Fourier Transform Infra-Red-Attenuated Total Reflection (FTIR-ATR), Thermogravimetric Analysis (TGA), contact angle, water uptake and ion exchange capacity. The inclusion of GO into the membrane proposed smoother and denser structures as compared to the PIM with no addition of GO. The peaks in the FTIR spectra of hydroxyl group (-OH) were diminished after the extraction occurred indicating that the -OH group was involved in the extraction via electrostatic interaction. TGA results demonstrated the degradation temperature of the bonds in GO-PIMs was delayed indicating the enhancement in membranes’ thermal stability after the addition of GO. High hydrophilicity of the PIMs was observed after GO was introduced, resulting to the contact angle value < 90o. Consequently, water uptake of the GO-PIMs showed an increment pattern with the highest value proposed by M5 (2.0 wt%) with 21.98%. In contrast, M5 performance was reduced in IEC value due to the aggregation happened at high concentration of GO. Thus, the highest IEC value was proposed by the M4 (1.5 wt%) with 1.23 %. Moreover, PIMs performance were evaluated in terms of gold extraction efficiency (E%) under different parameters such as different GO composition, different pH and initial concentration of feed solution. Surprisingly, the highest of E% was presented by M4 (1.5 wt% of GO) with 94.92% and the correlation coefficient show highest value for PSO model (R2>0.95) indicate the mechanism followed chemisorption.