Silver Recovery from Acidic Solutions by Formation of Nanoparticles and Submicroparticles of Ag on Microfiltration Membranes

Despite environmental regulations, wastewaters generated by some industries are in some cases discharged into lakes, rivers or reservoirs after inefficient treatments or without any pretreatment for the elimination or reduction of certain pollutants. Effluents may sometimes contain valuable elements with significant commercial value such as precious metals. Recovery of these metals is important because they could be harmful to aquatic life in lakes and rivers and because of its economic value. There are legal provisions regarding the composition of an effluent: in the case of liquids containing silver, it is a maximum of 5 ppm. It is known, however, that the silver ion could create a complex especially with thiosulfate, which has little effect on health. Even if silver would not affect health and there were no restrictions to its discharge, there is an important reason to recover it: its value and scarcity. Annual global demand for silver is currently of 24,500 metric tons, used in a vast array of industrial and consumer products. For example, silver is widely used in industrial electroplating as a protective coating or as adornment. Silver reflects light very well, so it is used in car headlights and mirrors. A laboratory that uses silver in its production could discharge monthly, a value of 150 to 1,800 dollars in silver. Worldwide, approximately 57% of the silver present in discarded products is recovered. It has the highest rates of recovery among the most commonly used metals, but much of it is still lost in the various emissions to the environment.