Comprehensive Recovery Of Valuable Elements From Zinc Vertical Tank Distillation Residue

Zinc produced through pyrometallurgical technology still takes a large portion of the yearly output in China, which acconuts for about one third of the total domestic metal zinc yield. Among the zinc produced by prometallurgy, the production of vertical tank distilling process takes up 20% or more. In comparison with world, it is the special feature of the zinc metallurgical industry in China.The recovering of valuable elements associated with the zinc sulfide concentrate is closely related to the mainflowsheet. For the hydrometallurgy of zinc, the main processing consists of roasting, leaching, purifying, and finally electrolyzing. Correspondingly the byproducts are recovered from roasting dust, leaching residue, purifying residue, and the multiple metal recovery technology has been successfully used in industry.While the comprehensive recovery of valuable metals in pyrometallgical processing of zinc is relatively insufficient.The vertical tank distilling zinc process includes oxidation roasting, oxidized ore and coke briquetting, vertical tank distilling and ingot casting. Large quantity of distillation residue was yielded during the vertical tank distilling process. Its output ratio nearly equates to the metallic zinc. The distillation residue contains about 30% carbon by mass and multiple valuable metal, such as zinc, lead, cadmium, copper and silver. Especially the silver, which associated with the zinc concentrate, almost entirely remains in the distillation residue. This kind of residue, if not given further treatment, can cause not only huge waste of energy but also great loss of valuable metal resources; what is more, may cause environmental problem due to the contained heavy metal.Therefore the development of new technology to treat the distilling residue has significant meaning for perfecting the vertical zinc smelting process.To recover both the high content of carbon and the multiple valuable metals remaining in the distilling residue, two different processing technology physical benification and vortex furnace fuming were tested in this paper.The main idea of physical benification is to firstly separate carbon from distilling residue and then the heavy metal minerals by utilizing their difference nature in density and floatability. But experiment results showed that neither shaking tables nor ultra-gravity centrifugal separator could achieve the separation and enrichment of the carbon or the heavy metal minerals. The flotation processing also failed to separate cabon or heavy metal minerals from the distilling residue. The presenting of large amounts of carbon in the distillation residue has strong adsorption to the mineral processing reagents, which constrained the reagents function properly.The study on fuming treatment of the distillation residue indicated vortex furnace is capable to treat the refractory residue. The energy of the carbon was effectively and directly utilized in the vortex furnace fuming process. About 1.99 tons steam of 0.8 MPa could be recycled as byproduct when treating one ton of the distilling residue. Meanwhile, vortex furnace has the advantages of large heat intensity and high processing capacity.The down-stream process choice for treating vortex furnace fuming slag and dust was mainly based on the practical production situation and especially the existing main flow of utilizing zinc smelting. The recycling of valuable metal from the fuming slag and dust was intended to join with the existing processing. The main purpose is to reduce the capital cost and achieve high efficiency, low cost and comprehensive recovery valuable elements from the distillation residue.During the fuming process of distillation residue in vortex furnace, the volatile components such as zinc, cadmium, lead and part of silver entered into the dust concentrate. Zinc in the fuming dust was extracted by leaching and finally was produced as marketable seven water zinc sulfate or zinc sulfate monohydrate products. The gross recovery of zinc is 89.00%. Along with the recovery of zinc, cadmium was separated as cementing residue in the purifying process using zinc dust. The cadmium residue was then sent to re-disolve, cement, distills and finally produced as refined cadmium product. The total recovery of cadmium was 92.11%. Lead and silver contained in the fuming dust were enriched in the leaching residue after extracting zinc and cadmium.This leaching residue served as raw materials for the lead and zinc ISF (Imperial Smelting Furnace) to recycle the lead and silver.The silver in zinc sulfide concentrates almostly reserves in the distillation residue. When posed to fuming treatment, only part of the silver enters in the dust and most is distributed in the fuming slag. To recover this part of silver the flotation method was tested. Both open circuit and closed circuit flotation experiments were carried out to separate silve from the fuming slag. The optimized flotation process was one stage roughing, four stages cleaning and three stages scavenging. The recovery of silver is 86.1% and the yield ratio of silver concentrate is 2.40% with a grade of 6100 g/t. The gold was also recovered in the silver concentrate with a grade of 4.8 g/t.The copper was recycled as copper matte intermediate prodcution when handling distillation residue in the vortex furnace fuming process. The copper recovery was 97.39%. The copper matte was periodically provided to the copper pyrometallurgical process for further treatment.The refractory distillation residue in vertical zinc smelting process can be effectively treated using vortex furnace fuming process. The heat energy of the residual carbon was efficiently utilized and the comprehensive recovery of valuable metals such as zinc, cadmium, lead, silver and copper was achieved. This new developed process provides effective method to the cleaner production of vertical zinc smelting technology. It doesn’t only enrich the varity of the enterprise’s products, but also enlarges the enterprise’s benefits. With a treatment of 0.15 million ton distillation residue in vortex furnace fuming process, a benefit of RMB 87.0396 million cab be gotten per year.