| China has become the largest country of producing and consuming zinc metal. Zinc resources in China have become more and more shortage as time goes on, and about one third of zinc raw material has to be imported, which has become one of the major factors to constrain sustainable development of society. Zinc resources, however, have not been utilized reasonably in China, especially the low-grade zinc oxide ore with high impurities like calcium and magnesium.Being a typical refractory ore in Yunnan province, Lanping lead-zinc ore has the characteristics of low grade, complex mineral textures, heavy sliming and high-content alkaline gangues. The zinc metal reserve of zinc oxide ore in the said area reaches about 4-million tons, which ranks the largest one in the world. The domestic research institutes have investigated it for many years, good flotation performance has been achieved in laboratory and pilot test, but the processing technology has not been put into commercial operation. Therefore, the run-of-mine ore has to be piled up or discarded, which has a capacity of 30-million tons up to now. There are two main reasons:first, if the ore is treated just by flotation, the high-grade zinc concentrate can be obtained, but its recovery is very low due to the poor processing efficiency of zinc oxide. In this case, the massive zinc metal are lost in the slime, resulting in waste of resources, which conflicts with the comprehensive utilization of resources advocated by circular economy. Second, the raw ore is directly processed by hydrometallurgy, not only will high-content alkaline gangues consume a large amount of acid, but also increase the energy consumption of zinc hydrometallurgical process. Therefore, it is necessary to improve the recovery of low-grade refractory zinc oxide ore and realize better utilization of the said ore as soon as possible, which has profound significance on utilizing the low-grade refractory ore and related industry in China.Under the technical background of circular economy, the new dressing-metallurgy combination process has been put forward, namely "calcium removal by flotation-preconcentration-zinc hydrometallurgy". The experimental results of studies on new dressing-metallurgy combination process signify that 86.56% recovery of total zinc for whole flowsheet that is the very good technical index. The acid consumption of rough zinc oxide concentrate is only 2.55t/t·Zn that is very low, which reduces significantly the acid consumption of zinc hydrometallurgy process. According with the three principles of circular economy, the new technology that can give full play advantage of flotation removing calcium as well as sulfuric acid leaching to recover zinc oxide minerals, and the goal of energy saving, emission reduction, comprehensive utilization of resources will be achieved. The recycling of wastewater produced in the dressing-metallurgy combination process has come true by using effective measures ultimately.The technology of zinc hydrometallurgy is a mature process, therefore, calcium removal by flotation and zinc preconcentration are researched mainly by the paper. The experimental results of studies on flotation process show that good performance can be obtained by using the separation process between slime and ore sand in the way of desliming prior to grinding. On the conditions of optimizing flotation process and adopting the efficient collector—HHA, good flotation index of rough zinc oxide concentrate can be gained:grade and recovery are 18.72% and 91.13% respectively, while the contents of calcium oxide in rough zinc oxide concentrate have declined from 22.23% to 12.31%. In this case,77.28% calcium oxide impurities in the ore have been removed. The process conditions of flotation are optimized by adopting response surface methodology, which provide the theoretical basis for choosing appropriate process conditions of slime and ore sand separation. A large number of experimental results show that pre-removing primary slime, using the modified collector—HHA, combined use of sodium carbonate and sodium sulfide are the key factors of success for the flotation process.The kinetics of sodium sulfide reacting with smithsonite and hemimorphite are studied by the paper in the flotation mechanism, and the sulfidation reaction rate equations on the condition of pH=9,10,11 respectively belong to the first-order reaction. It can be found that good recovery is achieved in high dosages of sodium sulfide for hemimorphite as a result of less adsorption and slow reaction rate on sodium sulfide. So it can be confirmed that more sodium sulfide are consumed due to high-content zinc silicate in the zinc oxide ore. The pure minerals experiments approve that recovery of hemimorphite can be enhanced by joint use of sodium carbonate and sodium sulfide, while calcite can be restricted strongly.All in all, the new process has great significance for increasing the utilization of low-grade refractory zinc oxide ore, releasing the shortage of zinc resources and realizing the sustainable development of zinc industry.
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