Low-grade chalcopyrite ore, heap leaching or smelting recovery route?
Introduction
Chalcopyrite, the most common copper mineral, is typically concentrated through froth flotation followed by the extraction of copper metal pyrometallurgically, through smelting/converting and electrorefining processes. Higher copper recovery and byproduct credits of silver, gold and molybdenum result in lower operating costs and higher sales revenue (per tonne of copper cathode) in pyrometallurgical treatment of chalcopyrite concentrates compared to the hydrometallurgical route. However, high capital cost and low flexibility in pyrometallurgical extraction of low-grade ores limit the treatment of chalcopyrite to the cut-off grade concentration. The capital investment for a pyrometallurgical plant was reported 10 times higher than the capital cost required to build a hydrometallurgical plant. For example, the fixed capital investment of a pyrometallurgical plant producing copper cathode from 0.5% Cu ore was reported US$30,000 per annual tonne of copper production (Schlesinger et al., 2011). Peacey et al. (2004) reported the capital cost of a HM plant with capacities between 40,000 Mt./y to 200,000 Mt./y to be around US$4000 to US$5000 per annual tonne of copper cathode. For smaller size plants, the capital cost was found higher per tonne of copper cathode production. For example, the financial data published recently show a fixed capital investment to vary between US$6980 to US$4948 per annual tonne of copper cathode for HM plant capacities between 7000 and 3000 Mt./y (Mokmeli, 2020).
High capital cost of the larger PM plants has encouraged copper producers to invest building smelters with lower annual production capacities specially in China. In 2019, about 36% of the copper produced pyrometallurgically was produced in smelters with lower than 200 kt/y comparing to the 25% in 2003 (Wang et al., 2019; Watt and Kapusta, 2019). In this regard, flash smelting, a suspension smelting technology, despite being a dominant technology, has seen a slight decrease in its share of world copper production since flash smelters are not suited for smaller size operations. In contrast, the bath smelting technologies including Suikoushan Bottom Blowing Smelting (SKS-BBS) furnace, Isasmelt and Ausmelt Top Submerged Lance furnaces and Vanyukov technology are currently used in the leading majority of global primary copper smelting operations that are mostly in a capacity range of less than 200 kt/y. The wide adoption of bath smelting technologies is mostly due to their lower capital cost investment (Gonzales et al., 2019).
On the other hand, as was also confirmed in this study, the operating cost of the HM plants are usually higher than that of PM plants. For example, Peacey et al. (2004) showed that the operating cost of a large smelter and an electrorefining plant is less than US$0.15/lb. while the heap leach/SX/EW operating cost is US$0.4/lb-US$0.55/lb. (in 2004). The practice on how to estimate the operating cost for a bio heap/SX/EW plant as a function of copper extraction efficiency, ore grade and heap acid consumption has been recently published by the author of this work, Mokmeli, 2020 (see section 3.3.1 of this study). In this study, the direct operating cost of hydrometallurgical treatment of a chalcopyrite ore with 0.28% copper content is shown to be varying between US$2.02/kg Cu to US$3.89/kg Cu for copper extraction efficiencies between 70% to 30%, respectively at a sulfuric acid price of US$90/t. In addition, the construction of a bio heap/SX/EW plant with production capacity of 7000 t Cu cathode required a capital investment of US$38.1 million in 2018. This is equal to an investment of US$2300(70% Cu recovery) to US$5400 (30% Cu recovery) per annual tonne of Cu cathode production.
The economic viability of a process varies depending on the operating cost, capital cost and the revenue from sales. In this study, technical and economic feasibility of treating 3000,000 t/year low grade chalcopyrite ore (CuFeS2 content >90%) through pyrometallurgical and hydrometallurgical routes were investigated. It is expected that at least a 100 million tonnes of low-grade run of mine ore, mostly chalcopyrite with the average analysis presented in Table 1, is available (rough estimate) at the waste dump areas at Sarcheshmeh mine, Kerman, Iran. For this amount, and with the treatment of 3000,000 t/year, 33 years of operation, in minimum, seems promising. At Sarcheshmeh copper mine the majority of the copper, 160,000 t copper cathode/year, is produced pyrometallurgically. The hydrometallurgy plant on the other hand, has a design capacity of 14,000 t copper cathode/year, but is operating below 50% of its capacity due to the issue related to depletion of oxide ores. Developing an economically efficient process to utilize the low-grade ores with the possible use of free capacity available at SX/EW plants or smelting/electrorefining plants, has been the motivation to this study. For this purpose, two scenarios were investigated. In the first scenario, construction of a new mineral processing plant to treat the low-grade ore was studied. In the second scenario, construction of a bio heap plant to treat the low-grade ore was considered. In both scenarios it was assumed that the downstream operations (SX/EW for the HM route and smelting/refining for the PM route) has the free capacity to absorb the upstream PLS or concentrate. A sensitivity analysis section discussed a more general scenario at which the construction of SX/EW and smelter/refinery plants are requiered.
The novelty of this work is the combination of the technical results based on a large pilot plant with economy of the process. In this research, the copper ore grade and its recovery (efficiency) corelated with the economy of the selected process. In this study, the importance of economy and factors such as discount rate were shown to profoundly affect the process selection such that the process with lower copper recovery can turn into a feasible process. The calculation methods employed in this study can easily enable interested researchers to follow the same approach using their own technical and financial data.
Section snippets
Experimental procedure
On average, 100 million tonnes of 0.28% copper ore with a known analysis of mostly chalcopyrite is available at Sarcheshmeh mine site. The average analysis of ore mineralogy is presented in Table 1.
In view of the low copper content of the above referenced ore and its particle size (10–20 cm), the preliminary possible recovery solution could be the bio heap leaching or the mineral processing/smelting processes. It is therefore important to investigate the feasibility of the two available options
Results and discussion
This section is presented in two parts. The first part covers the results obtained to examine the technical viability of both hydrometallurgical and pyrometallurgical routes. The second part of this study, economic feasibility, is comparing the economy of a pyrometallurgical route with the economy of a hydrometallurgical route. This part includes the estimation of the cash position, payback period and internal rate of return for both routes using the financial data reported in Table 8 and Table
Conclusion
This research was intended to link the process economy to the technical aspects of the recovery of low-grade high content chalcopyrite ore. In this regard, the ore grade and its recovery were corelated to process feasibility and it was shown that financial factors such as discount rate can profoundly affect the process selection, such that the process with much lower recovery may turn into a feasible process. For this reason, the technical data on a hydrometallurgical or pyrometallurgical
CRediT authorship contribution statement
Mohammad Mokmeli: Investigation, Methodology, Writing – original draft, Data curation, Supervision, Writing – review & editing. Masoumeh Torabi Parizi: Methodology, Data curation.
Declaration of Competing Interest
No.
Acknowledgments
The authors of this work wish to gratefully acknowledge the National Iranian Copper Industries Company for their support of this work.
References (16)
- et al.
Effect of the objective function in the design of concentration plants
Miner. Eng.
(2014) - et al.
Insights into heap bioleaching of low grade chalcopyrite ores-a pilot scale study
Hydrometallurgy
(2012) New developments in hydrometallurgical copper ore and concentrate leaching
(2019)- et al.
Comparison of Smelting Technologies, Copper 2019 Conference, 2019, Vancouver, Canada
(2019) - et al.
Process operating costs with applications in mine planning and risk analysis, Mineral processing plant design, practice and control proceeding
SME
(2002) Mining project finance explained, Mineral processing plant design, practice and control proceeding
SME
(2002)Prefeasibility study in hydrometallurgical treatment of low-grade chalcopyrite ores from Sarcheshmeh copper mine
Hydrometallurgy J.
(2020)Major mineral processing equipment costs and preliminary capital cost estimations, Mineral processing plant design, practice and control proceeding
SME
(2002)
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