不均化反応の利用による金の溶解と金微粉末の析出

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Dissolution and deposition of gold was studied for using the following equation (1) considered as a disproportionation of gold in a chloroaurate acid solution. 3 AuCl2- = 2 + AuCl4- + 2 Cl- …………… (1) An autoclave made of heat-resistant glass was used in the experiments. Gold wire was dissolved at a high temperature above 130°C by the reverse reaction of eq. (1) on the assumption of leaching gold scrap. After the dissolution experiment, the gold dissolved was recovered from the leaching solution by disproportionation in the cooling of the solution to normal temperature. At temperatures above 130°C, the gold wire easily dissolved in a 0.01 mol/l chloroaurate solution. It was considered that the dissolved weight showed an equilibrium concentration of AuCl2- in eq. (1). Though the concentration was small, it rose when the concentrations of Cl- or AuCl4- was heightened. The addition of Cl- had strong effect especially. Even with a small addition of 0.025 mol HCl-l, the dissolution weight of gold was elevated from 10-2 order g/l to several g/l. Namely, the effect for gold dissolution showed an increase of about 100 times. When the leaching solution of gold was cooled to a normal temperature, all AuCl2- ion formed by the reverse reaction of equation (1) was deposited as a metallic fine gold powder. There were submicron granular particles, fine particles with clear crystal faces and very thin flaked particles in the fine gold powder. It was clarified that these shapes were controllable by the cooling rate from the reverse reaction temperature to the disproportionation temperature.
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不均化反応の利用による金の溶解と金微粉末の析出

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