Removing metals from waste solutions with low rank coals and related materials

Abstract

Ion exchange media were produced by contacting brown coal, peat or wood sawdust with a solution of calcium hydroxide, preferably as an aqueous slurry of lime. The resultant calcium loading on the media, which ranged up to 8% for sawdust, 12% for peat and to 19% for brown coal, was exchanged for many metals in solution. Preliminary work showed the method to be amenable to extraction of copper, nickel, chromium, cadmium, lead, zinc, mercury, cobalt, silver, iron, manganese, vanadium, germanium, gallium, aluminium, antimony and uranium. For most of the metals more than 99% was removed from I g 1 −1 solutions. In more detailed work, confined to calcium loaded brown coal and solutions having metal concentrations more typical of industrial operations, minimum residual metal concentrations of 0.0005 mg l −1 mercury; 0.02 mg 1 −1 copper; 0.02 mg 1 −1 zinc; <0.05 mg l −1 cadmium; 0.1 mg 1 −1 lead and 0.2 mg l −1 manganese were obtained. These results compare favourably with those reported for other relevant processes and there might be operational advantages in the method. The method can be applied either by agitating the calcium loaded media in the solution and then filtering, or by passing the solution through packed beds of the media. Where appropriate, dilute solutions can be up-graded for re-use by stripping the metals from the media which can also be re-used. Alternatively, the loaded media can be combusted and the metals recovered from the residues. The method might be applicable to mine drainage and to effluents from metallurgical processing and electroplating, but more work is required to assess costs. It is suggested that the method is environmentally preferable to other common effluent treatment procedures because it enables collection and recycling of heavy metal pollutants.