Residual water is produced in different industries that use gold and silver and the recovery process is influenced by the metallic content and chemical properties of the effluent. Probably, the jewelry industry and electro-plating are the main sources of effluents that contain gold. For instance, here are various methods in operation among jewelers for the recovery of the gold from their waste waters and the old plan of dealing with these waste waters consisted merely of a moderately-sized tub for the collection of liquid substances of every kind employed in the manufactory; this tub was fitted with a tap about one-third from the bottom; precisely under this was placed a circular framework, of sieve-like form, with a rather closely-fabricated piece of felt or flannel attached loosely to the rim, so constructed as to form a cavity in the centre for the collection of the liquid, as it issued slowly from the tap immediately above it.
After filtering the effluent, it was allowed to run away, no more notice whatever being taken of it. Now this liquid carried along with it a considerable portion of gold. With the years, some improvements subsequently effected, or rather, presumed improvements were done; and metallurgists began to pay special attention to the economy of the process, with the view of reducing the working loss to the lowest extent possible, compatible with safe working. This loss was considered excessive, in proportion to the quantity of manufactured articles produced out of a given quantity of material; and a comparison of weights showed such to have been actually the case. To economize the treatment has been important to handle properly the chemical reagent and solution generated in the process.
Several large vessels were to be provided differing in sizes, and placed in a row, each succeeding one to be smaller than the preceding. In each of these tubs taps were to be fitted, which could be turned at any time. First of all the water would have to be conveyed by piping, from the several workshops connected with the manufactory, into the largest vessel; when this had become full, the tap could be turned on and all the surplus water carried over into the next, and so on, until the last in the row was reached; and in this, a piping in place of the tap must be firmly secured, to transport the whole of the liquid, after its passage through the row of vessels, into a large tank of deal. The latter part could be conveniently performed by placing some care yard or some outbuilding belonging to the premises, where the excess of water might drain away. It was supposed that by this means the whole of the gold would be recovered, on the ground that the passage of the water through the tubs would be so checked, and so slow, that the small particles of gold would all sink to the bottom, and thus be eventually recovered.
It is important to indicate that in the jewelers acids and other waste liquids, there are minute pieces of gold, which no amount of filtering, or passing through a series of vessels of stagnant water can possibly recover, unless some chemical ingredient be added thereto, which has the power of reducing the gold to its metallic state. For it should be understood that the dissolved gold and there is a considerable quantity in the residual waters passes through the filter as freely as the liquid itself. Therefore, unless this is acted upon chemically, no hope can possibly be entertained of its ultimate recovery.