Mineral processing: Key to export led industrialization
By Hlanganipai Ngarivume
The predominant minerals extracted in Zimbabwe include; Platinum Group Metals (PGMs), base metals, gold, diamonds, ferrochrome, asbestos, iron, tin, tantalite, coal, phosphate and lithium. The high level of mineral endowment could catalyze wider economic development and industrialization of the country. This is achievable if the minerals regime is overhauled and effectively administered to maximize all of the developmental opportunities associated with mineral extraction and processing through creating a backbone of a vibrant metallurgical and manufacturing industry. Currently Zimbabwe mineral exports are predominantly raw ore (run-of-mine ore) or semi-processed minerals (concentrates) which are low value added products as far as export earnings are concerned. Government effort, through the beneficiation thrust, focuses on establishing a limited transformation downstream from mining, including smelting and refining. Comparatively, this differs from South Africa’s beneficiation industry which includes the transformation of metals and other final products of mining and mineral processing into manufactured products. Hence, the long term goal of the beneficiation and value addition policy of Zimbabwe should be to provide a linkage to manufacturing.
However, the current government beneficiation thrust is realistic basing on the current state of the industry lest we might end up, “biting off more than we can chew”. One step at a time in the right direction is always good progress. In this article, the focus is on explaining the basic practical fundamentals of mineral processing in value addition and how the field of metallurgy can be employed to effect meaningful export through embracing downstream processing. Therefore, the aim is to point out the factors that need to be addressed for Zimbabwe to effectively embrace downstream processing in order to drive to a conclusion that will help us address our debate on “meaningful export led industry.”
Zimbabwe’s minerals sector accounts for about 12 % of the country’s gross domestic product (GDP) and the government is targeting to generate US$12 billion annually by 2023. For this to be achieved, the government must address challenges such as persistent power shortages, foreign currency shortages, and policy uncertainties (The International Trade Administration, 2021). According to the International Trade Administration (2021), foreign currency retention requirements have disabled mineral exporters, mainly at times when the black-market exchange rate deviated greatly from the official rate and has incentivized smuggling.
Mineral processing or mineral beneficiation is defined as the art or science of treating crude ores and mineral products in order to separate the valuable minerals from the waste rock, or gangue (Kapadia, 2018). Downstream processing from the ore or concentrate stage usually involves weight reduction by two-thirds for copper and by three-quarters for bauxite/aluminum, less for most other minerals, so lower freight costs should in principle be a powerful incentive for further processing. Let’s consider platinum as a case in point with Zimbabwe being the third largest producer of platinum in the world. Platinum has four levels of beneficiation which are; concentration, smelting, converting and metal refining. Out of the three platinum mines in Zimbabwe, presently none is doing metal refining. Zimplats and Unki mines are going up to level three (converting) and level two (smelting) respectively. Mimosa mine is going as far as level 1 (concentration).
The process of platinum concentration would include crushing, milling and froth flotation. Froth flotation takes advantage of the different physicochemical surface properties of minerals in particular, their wettability, which can be a natural property or one artificially changed by chemical reagents. By altering the hydrophobic (water-repelling) or hydrophilic (water-attracting) conditions of their surfaces, mineral particles suspended in water can be induced to adhere to air bubbles passing through a flotation cell or to remain in the pulp. The air bubbles pass to the upper surface of the pulp and form a froth, which, together with the attached hydrophobic minerals, can be removed. The tailings, containing the hydrophilic minerals, can be removed from the bottom of the cell. This process will basically get rid of the high mass gangue material leaving us with a concentrate high in the Platinum Group Minerals (PGMs) and base metals. Processing of PGMs is summarized in the figure below.
Typical process flowsheet for PGM ore processing (Mpilonhle, 2018)
This concentrate is then taken for smelting, converting and refining; the objective being to separate the base metals from the PGMs. Smelting is an extractive metallurgy technique that uses heat to remove impurities or gangue minerals from the ore (Mpilonhle, 2018). The process takes place under high temperatures in an electric furnace. Oxygen is blown into the system which will be under high temperatures to react with the Sulphur in the concentrate, thus producing an off-gas of Sulphur dioxide. The Sulphur dioxide can be trapped for the manufacturing of sulphuric acid. The product from the smelting process is known as matte.
Converting may be considered as a secondary pyrometallurgical process. In primary processes the concentrate or ores are brought to a molten state in other vessels, whereas in converting, the molten material is further processed by air as a medium to oxidise the material. The process follows smelting and is done to further remove iron as iron oxide and sulphur as sulphur dioxide. Sulphur dioxide is removed as an off-gas, and iron oxide is removed as part of slag. Converter matte (white matte) is the required output which is then taken for metal refining.
In the refining stage, the converter matte is the feed material to be purified. In common use is the dissolution-precipitation (pressure oxidation leach), solvent extraction and/or ion exchange and molecular recognition technology. Dissolution of the base metals occurs, while the PGMs remain in the residue. The PGM residue is then taken to a precious metal refinery for the separation of individual metals. Our products will be PGMs and gold as the precious metals then base metals in the form of nickel, copper, cobalt, nickel e.t.c. The next unit operation in the value chain will be manufacturing and fabrication of auto catalysts, dentistry equipment, resistance thermometers, jewellery, gas turbines, coins and other industrial end products.
At this point it is important to note that the procedures described above apply to most precious and base metals the only difference being process parameters. For instance; copper, nickel, and cobalt are all refined using more or less the same procedures described above. This therefore drives to the fact that the requirements in terms of capital and/or policies to foster for downstream processing runs almost across all minerals mined in Zimbabwe.
The upside of downstream processing which makes it key to export led industrialization is that; prices of products may be more stable. An end or refined product tends to hold price over time as compared to ore or intermediate products that always have price fluctuations due to constant changes in supply and demand. Further processing would therefore provide some assurance against revenue variations. On the other hand, the processed minerals may be strategic or, at least, less expensive, inputs for domestic manufacturing, construction, or agriculture. Imagine how Zimbabwe is a farming nation and we have a mine such as Dorowa Mine producing phosphate up to the stage it can be consumed by farmers as fertilizer. The chain can perfectly stretch in such a way that mining will enhance agricultural products exportation.
So many advantages can be related to downstream processing but the fact that it is still not happening in Zimbabwe can be interpreted to mean that the playing field is not level. Thus efforts must be driven towards the following factors to ensure that downstream processing makes business sense.
Availability of inputs; Inadequate supply coupled with a fairly high cost of electricity will push the cost of beneficiation and value addition up. It is difficult to run smelters and refineries discussed in this article competitively without low cost electricity. A case in point is the Democratic Republic of Congo listed issue, where a legal requirement to process copper concentrate was delayed after copper producers demonstrated that there was not enough electric power available to smelt and refine the copper mined in the country (Creamer Media, 2016).
This point leads us to another crucial aspect of scale factor. Many industrial processes require large scale to be commercially viable. The plants are of high capital expenditure and as such, the output to be treated must also be optimized for positive NPV and payback. If the available production of raw minerals is not sufficiently large, downstream processing is not economically feasible. For instance, a copper smelter needs access to about 150,000 tons of copper concentrate or more per year to be commercially viable. New crude steel plants using blast furnaces generally have a capacity of at least 2 million tons per year. Meaning it is very important to ensure that our extraction processes have been fully mechanized in order to meet the expected production.
Business environment factor is obviously of importance. Besides the obvious fact that mines have to be located where there are mineral deposits, it is important to ensure that vital resources and policies are in place to encourage investment. Factors such as availability of skilled labour, logistics, and financial services are very noble in making investment decisions. This factor is the one that, in principle, governments can influence most easily in addition to political risk considerations. In addition to the above, there is need to establish markets for the end refined products. There is emerging competition from recycling and also growing use of PGMs in general.
In conclusion, it is important to recognize that mining is a business and any decision made to influence operations has to make feasible sense. Therefore, it is important that government implements functional policies. As it stands, the beneficiation and value addition strategies as contained in the National Development Strategy 1 (NDS1) if implemented will go a long way to promote the export led industrialization drive. Producers usually have to be given positive incentives to invest in processing capacity which could be relaxation of taxes and import charges on capital inputs. It is important that as a nation we properly align ourselves to the demands of downstream processing as understood within and beyond this article.
About the author
Hlanganipai Ngarivume is currently the Head of Metallurgy Department at the Zimbabwe School of Mines (ZSM). The author can be contacted on email@example.com; +263 71 308 0008.