The most effective leaching agent for the recovery of gold and silver from electronic waste using hydrometallurgical techniques is a combination of Aqua Regia and Cyanide solutions. Aqua Regia, a mixture of concentrated nitric acid HNO3 and concentrated hydrochloric acid HCl in a 1:3 ratio, is highly effective in dissolving gold due to its strong oxidizing nature. It forms a soluble gold complex, chloroauric acid HAuCl4 , which can be easily separated from the remaining solid waste.For silver recovery, cyanide leaching is the most common method. A dilute solution of sodium cyanide NaCN or potassium cyanide KCN is used to form a soluble silver complex, dicyanoargentate [Ag CN 2]- , which can be further processed to recover the silver.However, it is important to note that both Aqua Regia and Cyanide solutions are highly toxic and corrosive, and their use requires proper safety measures, waste management, and environmental considerations. Alternative, less toxic leaching agents, such as thiourea, thiosulfate, and ionic liquids, are being researched for their potential in gold and silver recovery from electronic waste.