Rate of Leaching from Rare Metal Ore

点击翻译按钮获取中文摘要

Experiment has been conducted for the leaching from roasted zinc ore and nickel oxide ore by sulfuric acid in a stirred tank. Kinetics for the leaching has been discussed on the basis of observed results.The leaching from zinc ore is characterized by two stages: the first stage "leaching A" resulting from the leaching of zinc oxide; the second, "leaching B"from the leaching of zinc-ferrite. The first stage is very rapid, since the extent of leaching of zince, copper, and cadmium at 100 sec attains to 94, 60, and 77 %, respectively. The rate of leaching is higher in the order, cadmium, copper, and zinc, being affected more by temperature and the size of ore particle. In the second stage, cadmium, copper, iron, and zinc are leached at almost the same rate which is so low that complete leaching requires about 12 hr.In the leaching from nicked oxide ore, nickel, cobalt, magnesium, and iron are leached at similar rate, though chromium at very low rate. The extent of leaching at 60 min, almost at a terminal stage, is 90 % for nickel and magnesium, 80 % for cobalt and iron, and 17 % for chromium. The leaching rate is influenced much by temperature and acid concentration, but not so much by the size of ore particle.The unreacted-core model can be applied to the leaching of zinc in the first stage "leaching A" for the roasted zinc ore, but not to those of copper and cadmium. The fact suggests that copper and cadmium, unlike zinc, are nonuniformly distributed in the ore. As for the explanation of the second stage "leaching B" for the zinc ore and the leaching from nickel oxide ore, the volume reaction model can be adopted: Activation energy for the leaching ranges from 17.4 to 23.1 kcal/mol, which implies that a rate-determing step in the leaching is chemical reaction.