Outotec® Direct Zinc Smelting Process

Zinc production from sulphide concentrates has traditionally been achieved via the Roasting – Leaching – Electrowinning (RLE) flowsheet. This processing route, however, is associated with the generation of large quantities of hazardous leach residues which cause environmental issues in terms of residue handling and storage, along with increased losses zinc and other metal values.

The Outotec® Direct Zinc Smelting (DZS) process provides a means for the direct pyrometallurgical treatment of zinc sulphide concentrates to produce a high-purity, oxide fume and low zinc content discard slag. The process is particularly well suited to the processing of low-grade concentrates with significant concentrations of gangue impurities such as SiO2, CaO and MgO, thereby overcoming the limitations of the Roast-Leach-Electrowinning (RLE) flowsheet.

The DZS process incorporates separate smelting and reduction operations, which may be carried out in a batch-wise fashion in a single Outotec® Ausmelt furnace, or alternatively in a continuous manner in two (2) separate furnaces (Figure 1).

Figure 1: Flowsheets for the Outotec® Direct Zinc Smelting Process

Development of the DZS process has been carried out at the Outotec pilot-scale testwork facility in Dandenong, Australia. Demonstration of the process was recently carried via a series of 12 trials for a Bolivian customer in late 2015.

The Outotec® DZS process was also successfully demonstrated in 2013 at the Yunnan Tin Company Ltd. (YTCL) Lead Plant in Gejiu, China (Figure 3). Utilising a two stage, batch operation in a single Ausmelt furnace, 760 tonnes of zinc concentrates were treated over a period of 5 days. Commercial scale demonstration of the process indicated an expected zinc recovery of 97 – 98%, with slag tapped at the end of reduction containing on average, less than 2 wt. %. Recoveries of lead, tin, silver, indium and germanium were also very high (90 – 95%) and considerably better than those achieved with the RLE flowsheet.

Figure 2: Ausmelt Furnace at the YTCL Lead Plant

Outotec has also carried out extensive laboratory-scale testing of a tailored leaching process for the recovery of zinc and other metal values from fume generated from not only Direct Zinc Smelting, but also zinc leach residue treatment in the Ausmelt furnace. This work has led to development of a patented hydrometallurgical process flowsheet for the treatment of these materials (Figure 3).

Figure 3: Schematic Illustration of the Outotec Oxide Fume Treatment Process.

Text: Jacob Wood