Wohlwill Electrolytic Process
An old and well-established process, the Wohlwill method is widely used in major gold refineries, often in conjunction with the Miller process. (For typical jeweler's scraps and wastes, a preliminary refining step, such as the Miller or inquartation process, is required.) An electrolytic refining technique, it entails the electrolytic dissolution of an impure gold anode in a hydrochloric acid-based electrolyte. The process results in a deposition of 99.99 percent pure gold at the cathode. The silver and insoluble PGMs (along with a little gold) fall out as anode slimes, with the silver precipitated out as silver chloride, and all are recovered later. Any base metals, platinum, and palladium remain in solution, and can be treated later to recover the PGMs.
Gold of a purity of at least 98.5 percent is normally required for the anode, as too much silver will result in silver chloride building up on the anode surface and preventing dissolution of the gold. Typically, the input material for the anode is the gold from the Miller process, described previously.
Because it is time consuming-typically 24 hours or more-and suffers from the lock-up of gold inventory in the electrodes and electrolyte, the Wohlwill process is not suitable for small-scale refining.
An old and well-established process, the Wohlwill method is widely used in major gold refineries, often in conjunction with the Miller process. (For typical jeweler's scraps and wastes, a preliminary refining step, such as the Miller or inquartation process, is required.) An electrolytic refining technique, it entails the electrolytic dissolution of an impure gold anode in a hydrochloric acid-based electrolyte. The process results in a deposition of 99.99 percent pure gold at the cathode. The silver and insoluble PGMs (along with a little gold) fall out as anode slimes, with the silver precipitated out as silver chloride, and all are recovered later. Any base metals, platinum, and palladium remain in solution, and can be treated later to recover the PGMs.
Gold of a purity of at least 98.5 percent is normally required for the anode, as too much silver will result in silver chloride building up on the anode surface and preventing dissolution of the gold. Typically, the input material for the anode is the gold from the Miller process, described previously.
Because it is time consuming-typically 24 hours or more-and suffers from the lock-up of gold inventory in the electrodes and electrolyte, the Wohlwill process is not suitable for small-scale refining.
