Marble waste as attenuator of acidic effluent

Abstract

Dimension stones are worldwide used as building and finishing material, reason why the environmental problems inherent to this productive sector became relevant in various countries. One of these problems is the production of large amounts of wastes during the sawing of rocky blocks and polishing of plates. The waste generated by cutting marble with diamond wire consists of fine particles of calcium and magnesium carbonate dispersed in water. This mud has basic character, and it is destined to drying beds or open pit deposits. In parallel, many production processes generate hazardous acidic effluents, which disposal is a serious and global problem. The pH of these solutions must be neutralized or, at least, raised to levels that are considered safe by environmental regulations. In this work, a strong acid solution was treated with varying amounts of marble waste coming from the dimension stone industry. The treatment generated secondary solid and liquid phases that were analyzed to determine the feasibility of their disposal in landfills. The waste raised the pH of the acid solution from near 1.0 to values between 5.0 and 6.0, which are acceptable levels for non-dangerous effluents. Besides that, loss of up to 50% in mass occurred, diminishing the amount of the primary solid waste. By the other hand, the levels of total dissolved solids (TDS), Cu, chlorides and nitrates on the liquid phase of the effluent remained higher than that allowed by environmental legislation for discharge into water bodies. Nevertheless, their characteristics correspond to non-hazardous and non-inert wastes, which, after dried, can be discarded in ordinary waste landfills.