Treatment of a platinum leachate by membrane distillation: Mechanism of combined silica scaling and organic fouling for distinct system performance decline

Platinum (Pt) is an important rare element and has been widely using in electronic industry, chemical industry and defense industry due to its unique physicochemical properties. Given the high cost of exploiting Pt from limited natural ores, it is desirable to recover Pt from secondary resources for sustainable development. In this study, direct contact membrane distillation (DCMD) was employed to treat a real acidic platinum leachate (PL) with high-salinity. Results of membrane autopsy and silica-membrane interaction revealed that DCMD system performance decline in varying degrees was due to combined silica scaling and organic fouling. Importantly, it was found that the mass-to-charge ratio (m/z) range change of organic compounds in PL had significant effect on system performance. The low molecular compounds in PL with m/z value distributed in a smaller range from 100 to 200 at pH of 1, 3 and 7 possibly resulted in the membrane pores blockage, which was the main reason for the permeate fluxes rapid decline during DCMD process. Despite high molecular compounds with m/z value ranging widely from 100 to 600 detected in the concentrated PL, there was negligible effect on permeate flux decline in the initial stage at initial pH of 5. Deterioration of DCMD performance at pH of 5 was mainly due to accumulated silica scaling caused by the lower concentration of silica.