"When to do a cleanup". Still, a large, visible amount of black sand being present is not necessarily a sign that you are losing gold. Gold is about four times heavier than black sand. As long as there remains fluid action behind the riffles, the black sand might have little or no effect upon gold recovery.
The purpose of this study was to develop a resource recovery procedure for recovering copper and zinc from dust produced by copper smelting furnaces during the manufacturing of copperalloy wires. The concentrations of copper in coppercontaining dust do not meet the regulation standards defined by the Taiwan Environmental Protection Administration; therefore, such waste is classified as hazardous.