Passive treatment of arsenic and heavy metals contaminated circumneutral mine drainage using granular polyurethane impregnated by coal mine drainage sludge

A one-step and facile process was used to incorporate coal mine drainage sludge (CMDS) into granular polyurethane (PU), designated as PUCMDS, to remediate circumneutral mine drainages simultaneously contaminated by arsenic and heavy-metals. PUCMDS was characterized through physiochemical analyses. Several batch and column tests were carried out. CMDS was homogeneously stuck on the large-sized pore surface of PU. Based on the kinetic modeling, the low-range Biot number (BN, 0.86-2.63) indicated that external diffusion is a main rate-limiting step. Rapid small-scale column tests (RSSCTs) also showed this phenomenon, in which the empty bed contact time (EBCT) influenced the arsenic removal efficiency more than did the PUCMDS size. PUCMDS had 8190-14,330 bed volumes (BVs) of breakthrough (BT, 50 μg L−1) for As(V), while it did not have BTs for other heavy metals, except for Fe(III). Two pilot-scale columns were conducted to observe their outlets till 7644 and 3800 BVs. As a result, PUCMDS did not have any BTs for all regulations of As (total) and heavy metals. All results in this study demonstrated not only that PUCMDS can effectively remove arsenic and other heavy metals in circumneutral mine drainages, but also that it shows an example of sustainable development concept in mine sector.