شبکه فرآیند هیدرومتالورژی روی
Abstract
Graphical abstract
1. Introduction
2. Method
3. Results and discussion
4. Conclusions
Acknowledgment
References
Abstract
Heavy metals could serve as both pollutants and resources. To better understand the cleaner production potential of material flow control for simultaneous pollution reduction and resource conservation at source in zinc hydrometallurgy system, the generation and distribution of the Pb, Cu, and Ag in the process network of a typical zinc hydrometallurgy plant were investigated in this study. Four kinds of hazardous wastes with a total dry weight of 942 kg/tZn were identified as the major system outputs for Pb (12.08 kg/tZn), Cu (5.63 kg/tZn), and Ag (70.5 g/tZn). More than 85% of the target substances were accumulated in the leaching and purification subsystem, which determined the final proportion of the substances in the system outputs. The unsatisfactory distribution of the substances in the present process network contributes 0%, 45.9% and 27.5% of final resource wastage or pollution for Pb, Cu, and Ag of the generated wastes, corresponding to 0, 0.53 kg/tZn, and 13 g/tZn, respectively. Presently the Pb wastage or generation of Pb pollution was mainly due to the lack of recovery process. However, the potential to optimize the flow partitioning for Cu is relatively high. In summary, optimization of the process distribution might slightly increase the total recovery rate of the substances, but could significantly reduce the environmental risk of the disposed wastes generated in the zinc hydrometallurgy system. These results will be helpful to improve the understanding of the mechanisms for heavy metal pollution generation and provide further insight in the control of pollution and resource in process industries, such as nonferrous metals industry
Introduction
The industrial application of metals continually increased during the 20th century, with around 60 metallic elements in use today (UNEP, 2011). Heavy metals produced by industrial activities is one of the most important environmental problem at present (Zhang et al., 2018). Zinc is the fourth most widely used metal after iron, aluminium and copper (Abkhoshk et al., 2014). The production of refined zinc in 2017 is up to 13 million tonnes (CNMIA, 2018), and the demand for zinc is expected to remain strong in the coming years due to the growth in the numbers of zinc consuming industries. Presently, more than 85% of the zinc metallurgy is produced by hydrometallurgical technology (NDRC, 2016). Zinc hydrometallurgy has a typical production procedure known as Roast-Leach- Electrowinning (RLE) process (Fuls and Petersen, 2011), which was hailed as an environmentally friendly alternative to zinc pyrometallurgy due to the lower energy consumption and less pollution to the atmosphere in the past. However, discharge of the solid wastes which contained heavy metals which might be far from inert is one of the most significant environmental drawbacks in the zinc hydrometallurgy industry (Anthony and Flett, 1994). Zinc hydrometallurgy system is a highly interconnected system with many of the metals being derived from the zinc ores and as byproducts. Almost all the associated metals, such as Fe, Pb, Cu, Ag, Cd, Co and Ge, imported accompanied with the raw material (e.g. zinc calcine) were emitted by zinc hydrometallurgy system as metabolic byproducts (Khosravi et al., 2018).