LANDFILL LEACHATE AS A FROTHER AND COLLECTOR IN FROTH FLOTATION

摘要

Landfill leachates are highly polluted wastewaters resulting from the ingress of water to landfilled municipal solid wastes and the degradation and leaching of materials from the wastes. They are highly variable in composition between sites and with time. They contain biodegradable compounds, inorganic salts and trace recalcitrant pollutants. Normally, in the waste management industry, they require treatment for the reduction of their biochemical oxygen demand (BOD), chemical oxygen demand (COD) and ammoniacal nitrogen contents prior to release to the environment. It has been found that landfill leachate can substitute for some, or all, of the frother and collector additions necessary for the effective operation of some froth flotation systems. It is thought that the volatile fatty acid (VFA) content of landfill leachates accounts for the frothing and collecting action. Younger leachates performing relatively better than older leachate samples, since bacterial action reduces the VFA content in older leachate samples. The desirable organic components of landfill leachate can be concentrated by membrane filtration, greatly reducing the associated transport costs and the volumetric additions necessary for effective flotation. Landfill gas condensates offer an alternative, purified and often concentrated source of VFAs. The filtrate after the flotation process employing landfill leachate has greatly reduced biochemical oxygen demand (BOD), due to the removal of the VFAs by adsorption onto mineral surfaces and in the froth phase. Ammoniacal nitrogen in the landfill leachate remains in the water phase and will form part of the composition of the moisture content of tailings requiring disposal. The level of ammoniacal nitrogen present is appropriate to promote vegetation of the tailings streams. The results of flotation testwork, with both raw leachate and nanofiltration concentrates, is presented, together with a discussion of the potential benefits in tailings vegetation.