Adsorptive Removal of Pb(II) and As(V) from Aqueous Solution by PVDF/HMO Ultrafiltration Mixed Matrix Membrane

Lead and arsenic are among the designated chemicals of major concern by the World Health Organization, they affect millions of people worldwide with both acute and chronic effects on human health. In the current study, mixed matrix membranes (MMMs) were fabricated using polyvinylidene fluoride (PVDF) for the matrix and hydrous manganese dioxide nanoparticles to remove lead, Pb(II), and arsenic, As(V), form water. The objectives of the study were to fabricate membrane with HMO:PVDF ratios from 0 to 1 and to characterize their adsorption properties on the two metals and their filtration performances. The HMO nanoparticles were synthesized using manganese sulfate monohydrate and potassium permanganate. The membranes were fabricated using phase inversion, a dope solution was prepared with HMO:PVDF ratios between 0 and 1, NMP as a solvent at an NMP:PVDF ratio of 5.57 and PVP at a PVP:PVDF ratio of 0.1 to increase the permeance of the membranes. The dope solution was casted and then soaked in a water coagulation bath for phase inversion. The structure of the nanoparticles was observed using TEM, and the structure of the membranes was described using SEM. The adsorption tests assessed the adsorption capacity, the adsorption kinetic and the effect of the pH on the adsorption capacity for the two metals. The concentration in the samples was measured with ICP-OES. A FTIR analysis was performed as a proof of adsorption. The tests that were run to assess the filtration performance of the membranes were the following ones: pure water permeance test, hydrophilicity test, surface analysis using XPS, pore size with AFM and finally filtration capacity on lead and arsenic. The HMO particles that were produced had sizes in the nanometer range and were elongated, which provided them a large surface-to-volume ratio. The membranes had asymmetric structures and the membrane with large HMO ratios had the surface of their pores covered uniformly with HMO particles. The adsorption capacities of pure HMO particles were 36 [mg/g] for arsenic and 283 [mg/g] for lead. The adsorption capacity of the membranes with an HMO:PVDF ratio of 1 was 11 [mg/g] for arsenic and 146 [mg/g] for lead. The Freundlich isotherm was used to describe the adsorption capacity of the membranes for both lead and arsenic. The adsorption kinetic was described by a pseudo-second order kinetic model for arsenic and the results were not significant enough the assess the adsorption kinetic model for lead. The equilibrium was almost reached in 30 minutes for the adsorption of the two metals on pure HMO. The adsorption capacity was enhanced with increasing pH for lead adsorption and it was the opposite for arsenic adsorption. The sensitivity to the pH was higher for lead compared to arsenic and this sensitivity to the pH could be used to regenerate the membrane in case of lead adsorption. The average permeance of the membranes was around 1500 [L/m2h bar], the pore sizes were in the ultrafiltration range, between 41 [nm] and 70 [nm] and the membranes were in the hydrophilic range, with an average contact angle of 69 [°]. The HMO ratio in the membranes had a limited impact on these three parameters. The filtration capacity on arsenic was too low to remove arsenic at ppb concentrations and the results of this test on lead were not significant enough to be interpreted.