Zinc Recovery of Low Grade Concentrate from Vazante Mine by the Waelz Process

摘要

Nexa Resources processes electric arc furnace dusts (EAFD) and other sources of secondary zinc at its Juiz de Fora unit, mainly by the Waelz Process. Aiming to increase the Waelz furnace feed, decrease stocks of the mines, and improve the company's recovery rate, a process to recover zinc from low grade concentrate produced at the Vazante mine that are not suitable for the traditional Roast-Leach-Electrowinning (RLE) process, due to the zinc content, were investigated in this study. The zinc concentrates, containing around 18-20% of zinc, were tested in a pilot scale Waelz furnace with the feed portion of 10 and 40% mixed with EAFD. Another input with 100% of this material was also investigated, and all tests were compared to the traditional feed of 100% EAFD. The parameters evaluated were zinc recovery yield and accretion formation inside the furnace. Other parameters of the furnace, such as reduction agent input, temperature, and residence time, were the same as the industrial Waelz process. The proposed process showed good response to accretion formation inside the furnace, such as with the increase in the portion of the low grade concentrate in the feed, and the accretions formation decreased. The technique was also efficient to zinc recovery yield with the feed portion of 10, 20, and 40% resulting around 92% of recovery. However, for the test feeding only the concentrate, the zinc recovery yield was decreased to 82%.