Water Requirements for Mining Operations in South Africa: A Focus on Mineral Extraction and Processing Methods

By Dr. DF Duvenhage

Introduction

South Africa is renowned for its rich mineral resources, contributing significantly to its economy. Mining has historically been a significant contributor to South Africa’s GDP. However, its exact contribution can vary from year to year based on factors such as commodity prices, production levels, and overall economic conditions. [1].

Figure 1: RSA GDP by sector

As of the most recent available data (Q4 2023), mining contributes about 5% to South Africa’s GDP, shown in Figure 1. However, it’s important to note that this contribution has decreased over the past few decades due to various factors, including a decline in the gold mining industry and increased focus on other sectors like services and finance. Mining remains essential to South Africa’s economy, providing jobs, export earnings, and crucial raw materials for various industries. The country is particularly rich in minerals such as gold, platinum, diamonds, coal, and iron ore, significantly contributing to its mining sector.

While mining’s contribution to GDP has declined somewhat over the years, it still plays a vital role in the economy. It remains a major focus for policymakers and industry stakeholders in South Africa. Mining contributes to employment in South Africa, both directly at mining activities as well as indirectly through service providers and contractors, as shown in Figure 2 [2] [3].

Figure 2: RSA employment per sector

However, the extraction and processing of these minerals come with substantial water requirements and challenges. The water demands vary depending on the mineral extraction type and the specific mining processes involved. For example, gold mining often involves heap leaching and milling, which require substantial water inputs [4]. Platinum mining encounters water inflows in underground operations and uses water-intensive processes like concentration and cooling [5]. Diamond mining relies on water for ore processing and recovery methods like dense media separation.Coal mining requires water for dust control, equipment cooling, and coal washing processes [6]. Iron ore mining involves water-intensive activities such as crushing, grinding, and pelletization [7]. Effective water management is essential to mitigate environmental impacts, ensure regulatory compliance, and support sustainable mining practices amidst South Africa’s water scarcity challenges. Mining companies increasingly adopt water recycling technologies and engage in community initiatives to reduce water consumption and environmental impacts [8].

This article explores the diverse range of minerals mined in South Africa and delves into the specific water demands associated with their extraction and processing.

Gold Mining

Gold mining has played a significant role in the history and development of South Africa since the first large-scale production began in 1873 with the discovery of alluvial deposits at Pilgrim’s Rest. However, it was the 1884 discovery of gold in the Witwatersrand region, shown in Figure 3, which truly transformed the country and led to an influx of miners from around the world [9]. The Witwatersrand Gold Rush began in 1886 and was a defining moment in South African history [10]. Prospectors established the existence of a belt of gold-bearing reefs 40 miles wide cantered on present-day Johannesburg [11]. By 1899, the gold industry had attracted investment worth £75 million (the currency of South Africa under British Imperial rule), produced almost three-tenths of the world’s gold, and employed more than 100,000 people, the overwhelming majority of them African migrant workers.

Figure 3: Gold reserves in RSA, https://www.mineralscouncil.org.za/sa-mining/gold.

The rapid growth of the gold-mining industry intensified processes started by the diamond boom, including immigration, urbanization, capital investment, and labour migrancy [11]. The first large gold mining company was established in 1886, and the development and population of Johannesburg increased ten-fold in just four years [9]. A new class, the Randlords, emerged as a result of the gold rush. Despite the challenges faced by the industry, including wars, strikes, accidents, and technical difficulties, South Africa’s gold mining industry has continued to thrive[2]. As of 2022, South Africa had 5,000 tons of known gold reserves, the most of any country in Africa [12].

The extraction of gold typically involves the following steps.

Exploration

Gold exploration is the process of finding economically viable gold deposits. It typically begins with a regional assessment of an area’s geology and known gold occurrences. Geologists use techniques such as geological mapping, geochemical sampling, and geophysical surveys to identify potential target areas. Once a promising area is identified, more detailed exploration methods, including drilling, are used to evaluate the gold deposit’s size, grade, and depth. Exploration is a crucial step in the gold mining process, as it helps determine a project’s feasibility and potential profitability. It requires significant investment and can take several years before making a decision to proceed with mine development. Successful exploration is essential for the long-term sustainability of the gold mining industry [13].

Construction

The construction phase begins once a gold deposit has been identified and deemed economically viable. This involves building the necessary infrastructure to support the mining operation, such as roads, power lines, water supply systems, and processing facilities. The construction phase also includes the development of underground tunnels and shafts if the deposit is located at depth. Building a gold mine can take several years and requires significant capital investment. Ensuring that the mine is designed and built to meet all relevant safety, environmental, and regulatory standards is crucial. The construction phase is also important for community engagement and ensuring that the local population benefits from the project. [13] [14].

Extraction

Gold extraction is the process of removing gold from the ground. Several methods are used to extract gold, depending on the deposit type and the ore depth. The most common methods are [13].

Drilling

Drilling is used to create holes in the ground to place explosives or to extract ore samples for analysis. It is typically used in underground mining operations or in areas where the ore is located at depth.

Blasting

Blasting is used to break up the rock containing the gold ore. It involves drilling holes into the rock and filling them with explosives, which are then detonated to create smaller, more manageable pieces of rock. Blasting is commonly used in open-pit mining operations.

Hauling

Hauling is the process of transporting the broken rock containing the gold ore from the mining site to the processing facility. It typically involves the use of large trucks or conveyor belts. The choice of haulage method depends on factors such as the size of the operation, the distance to the processing facility, and the terrain.

The section on platinum mining covers the challenges related to fisher water and water use for drilling in underground operations.

Transport

Once the gold ore has been extracted from the ground, it must be transported to the processing facility. The method of transport used depends on factors such as the location of the mine, the volume of ore being transported, and the infrastructure available. Common methods of transport include trucks, trains, and conveyor belts. Transporting gold ore can be a significant cost for mining operations, particularly if the mine is located in a remote area with limited infrastructure. It is important to ensure that the transport of ore is done in a safe and environmentally responsible manner. [13] [14].

Crushing and processing

Once the gold ore has been transported to the processing facility, it must be crushed and processed to extract the gold. The first step in this process is crushing the ore into smaller pieces to increase the surface area and make it easier to extract the gold. This is typically done using a series of crushers and mills. After crushing, the ore is processed using various techniques, depending on the type of deposit and the characteristics of the gold. Common processing methods include gravity separation, flotation, and cyanidation. These methods use physical and chemical processes to separate the gold from the surrounding rock and other minerals. The processing of gold ore is a complex and energy-intensive process that requires significant amounts of water and chemicals. It is important to ensure that ore processing is done in an environmentally responsible manner and that any waste products are properly disposed of or treated [13] [14] [15].

The flotation process involves creating a mineral concentrate by utilizing chemical conditioning agents, followed by vigorous agitation and air sparging of the agitated ore slurry to generate a foam concentrate rich in minerals. This method is credited to a miner who observed a similar process while washing soiled work clothing in a home washing machine. Specific chemicals are introduced to either float certain minerals or inhibit the flotation of others, with multiple processing stages typically employed to enhance product purity [16].

While the flotation process is not typically effective for floating free gold particles, it is particularly successful when gold is associated with sulfide minerals like pyrites. In cases of pyritic gold ore, the gold is enclosed within an iron sulfide crystal structure, with highly oxidized ores showing poor response to flotation. One of the advantages of flotation is that gold values are often liberated at a relatively coarse particle size, reducing ore grinding expenses. Additionally, the non-toxic nature of flotation reagents leads to low tailings disposal costs.

Flotation is commonly utilized when gold recovery is linked with other metals such as copper, lead, or zinc. The resulting flotation concentrates are usually transported to an external smelting facility to retrieve gold and base metals. Cyanide leaching is frequently combined with flotation, with the decision to cyanide leach flotation concentrates or tailings based on specific mineralogy.

The cyanidation process is the most used method for gold extraction and involves a leaching stage where cyanide dissolves metallic gold, forming a gold-cyanide complex and facilitating its separation from sand, rocks, and other minerals. Following this, two methods can be employed to reverse the process within the liquid solution, converting the concentrated gold-cyanide into metallic gold. One approach involves the precipitation of metallic gold through the introduction of zinc [17].

The cyanidation process typically involves percolation or agitation leaching of gold and silver ores using a dilute cyanide solution, generally less than 0.3 percent sodium cyanide. In industrial practice, the addition of lime to a cyanide pulp is a standard procedure to prevent hydrolysis and neutralize any acidic components present in the ore. Lime addition offers additional benefits, such as the decomposition of bicarbonates in mill water, improved settling rates in counter-current decantation thickeners, and enhanced extraction rates for specific ore types like tellurides and ruby silver.

The gold dissolved in the slurry produced by the above processes, is subsequently adsorbed onto granular activated carbon in the adsorption or carbon-in-pulp circuit. Activated carbon, essentially carbon (or charcoal) with tiny pores that enhance the available surface area for adsorption, facilitates this process. Adsorption refers to the mechanism by which molecules adhere to solid material. The carbon laden with gold is then extracted from the circuit and treated in an acid column to eliminate impurities from the carbon. Subsequently, the material is moved to the elution column, where it is immersed in a heated caustic cyanide solution. To extract the gold as a high-grade eluate solution, hot water is circulated through the column. The depleted carbon is then heated for regeneration and reintroduced into the circuit. The residual slurry (devoid of gold) is either disposed of in the Tailings Storage Facility (TSF) or directed to the Backfill Plant for the creation of the backfill material utilized underground [18].

Smelting and refining

The final step in the gold mining process is smelting and refining. Smelting is the process of melting the processed gold ore, along with a flux (a substance that aids in removing impurities), in a furnace to produce a molten metal mixture. This mixture is then poured into molds, which cools and solidifies into bars of impure gold, known as doré bars. The doré bars are then transported to a refinery, undergoing a series of processes to remove any remaining impurities and produce pure gold. The most common refining method is the Miller process, which uses chlorine gas to remove impurities [19]. Another method is the Wohlwill process, which uses an electrolytic process to produce high-purity gold. The refined gold is then cast into bars or coins or used to produce jewelry and other gold products. Smelting and refining are important steps in ensuring the quality and purity of the final gold product [15].

During the smelting process, water is used mainly to cool the furnace jackets. These furnaces are induction furnaces, which use electric currents to induce magnetic fields that heat the raw product and ultimately melt it. During the further refinement of the gold to reach a purity of 99.99%, water is used in various of steps to wash the products. Two popular methods used are the Miller and Wohlwill processes. The former involves blowing chlorine gas through molten gold to remove impurities, while the Wohlwill process further refines gold to high purity through electrolysis. The deposit on the cathode has a porous structure, necessitating a meticulous washing procedure to remove the entrained electrolyte completely. This process involves various hot water washes, followed by a sodium thiosulphate wash (to eliminate silver chloride) and additional hot water washes. The final product is then transported to the refining room, where it undergoes melting and casting into bars [20].

Platinum Mining

The discovery of the first platinum nuggets in South Africa can be traced back to 1924. The geologist Hans Merensky’s subsequent work identified two deposits, each approximately 100km long, which became known as the Bushveld Igneous Complex, as shown in Figure 4. This discovery began with test work in the area around Mashishing (formerly known as Lydenburg). Based on successive encouraging findings, Merensky approached a circle of friends to raise funds for investigating any potentially profitable platinum deposits. He used the farm Maandagshoek as a base and later secured 23 claims, working quickly to locate other platinum occurrences in the area. Merensky’s efforts resulted in the naming of the Merensky reef, and in 1925, follow-up work led to the identification of the eastern limb of the Bushveld Complex. The mines situated on this geological structure have, for many years, produced more than 75% of the world’s platinum output. Since World War 2, platinum mine production has grown continuously in response to the development of new applications for the metals. A significant new use of platinum was in the petroleum industry, where platinum catalysts were introduced to increase the octane rating of petroleum and to manufacture important primary feedstocks for the growing plastics industry. This was followed in the 1960s by a growing demand for platinum jewelry, given its purity, color, prestige, and value. In the latter half of the 20th century, the platinum sector in South Africa was dominated by Gencor, JCI, and Lonrho. Corporate actions eventually led to the mines in these groups being housed under Implats, Amplats, and Lonmin respectively, the majors in the sector, responsible for producing up to 80% of the world’s PGM supplies.

Underground mining operations encounter substantial water inflows that must be controlled to ensure safe working conditions. Additionally, water is crucial for processing platinum ore, involving flotation, smelting, and refining processes. The uses of water in platinum mining are very similar to those of gold mining; however, there are differences relating to the concentration, smelting, and refinement due to platinum group metals (PGMs) having vastly different material characteristics.

Figure 4: Platinum resources in RSA, https://www.mineralscouncil.org.za/sa-mining/platinum

Underground mining operations often encounter significant challenges related to fissure water, which refers to water that seeps through cracks and fissures in the rock. Managing fissure water is critical as it can cause flooding in mine shafts, weaken rock structures, and create hazardous working conditions. Water inflow can also interfere with mining activities and equipment, necessitating robust dewatering systems continuously pumping out water. Additionally, fissure water can carry dissolved minerals and contaminants, potentially leading to environmental concerns such as water pollution. Addressing these challenges requires comprehensive water management strategies, including advanced geological assessments, effective sealing techniques, and water treatment solutions to ensure operational safety and environmental protection [21].

Furthermore, using water for hydraulic drilling instead of compressed air offers potential energy savings due to the higher efficiency of hydraulic systems. Due to the great depths of platinum mine shafts, hydraulic drilling systems can deliver greater force with less energy than compressed air, reducing energy consumption and operational costs. The winders used to hoist the ore and personnel up and down in these deep shafts are shown in Figure 5.

Figure 5: A platinum mine in RSA, https://www.miningmx.com/news/platinum/27692-sibanye-implats-marriage-convenience-sa-platinum/.

However, hydraulic drilling introduces additional challenges related to water management. Water use necessitates comprehensive pumping and dewatering systems to manage the influx of water into the drilling site. These systems must continuously remove water to prevent flooding and maintain safe working conditions. The process involves substantial infrastructure and energy to operate pumps and treat the water, potentially offsetting some of the energy savings gained from using hydraulic drilling. Moreover, proper disposal or recycling of the water is essential to avoid environmental contamination. Hence, while hydraulic drilling can be more energy-efficient, the associated water management requirements need careful consideration to ensure a net benefit [22].

If hydraulic drilling is not an option and more conventional pneumatic drilling is required, water use becomes even more significant due to the cooling needs of above-ground multi-stage air compressors. Pneumatic drilling relies on compressed air generated by these compressors to power the drilling equipment. The compression process generates a substantial amount of heat, necessitating an efficient cooling system to prevent overheating and ensure optimal performance and longevity of the compressors.

Water is commonly used as a coolant in multi-stage air compressors to manage this heat [23]. This cooling process involves circulating water through the compressor’s cooling systems, absorbing excess heat before being either recycled or discharged. The intensive cooling demands mean that a continuous water supply is crucial, often resulting in significant water consumption. Additionally, the quality and temperature of the cooling water must be carefully controlled to maintain the compressors’ efficiency and prevent scale buildup and corrosion within the system.

Moreover, managing the heated water after it has passed through the cooling system presents further challenges. This water often needs to be treated to remove any contaminants before it can be safely discharged or reused, adding to the operational complexities and environmental considerations. Consequently, while pneumatic drilling remains viable, it entails a heightened reliance on water resources, emphasizing the need for effective water management strategies to mitigate the associated impacts.

Diamond Mining

South Africa is a leading producer of diamonds, primarily extracted from kimberlite pipes, which are vertical geological formations rich in diamonds [24]. The primary sources of all of South Africa’s diamonds are kimberlites found in ancient, vertically dipping volcanic pipes, predominantly situated near the city of Kimberley and initially suitable for open-cast mining. These deposits were largely unearthed in the latter part of the 19th century. In the early 20th century, the volcanic pipe of the Premier mine was discovered near Pretoria, and in the final decades of the century, the kimberlite pipe of the Finsch mine was found near the town of Lime Acres in the Northern Cape. Subsequently, the kimberlite of the Venetia mine was discovered near the town of Alldays in Limpopo province. Alluvial diamonds and small diamondiferous fissures have been recognized and exploited for many years along the southern banks of the Orange River, as well as along and offshore of South Africa’s west coast. These locations are shown in Figure 6.

Figure 6: Diamond mining activities in RSA

The extraction and processing of diamonds from these kimberlite pipes involve several water-intensive stages, each crucial for the efficient recovery of diamonds. Firstly, the ore must be crushed in large crushers as shown in figure ## to break it down into smaller, more manageable pieces. This crushing process often requires water to minimize dust and ensure smooth operation. Following crushing, the ore undergoes scrubbing, which involves using water to wash and remove any clay or soil adhering to the diamond-bearing rock. This step is essential to prepare the ore for further processing and improve the efficiency of subsequent stages.

Figure 7: Example of a diamond processing plant, https://www.cdegroup.com/applications/other-applications/mining-mineral-ores/diamond-processing

After scrubbing, the ore is screened to separate it into different size fractions. Screening is a water-intensive process where water helps to clean and separate the material based on size, ensuring that the diamonds are not lost and are effectively segregated for further processing.

One of the most water-intensive methods used in diamond recovery is dense media separation (DMS) [25]. In DMS, the crushed and washed ore is mixed with a slurry of ferrosilicon and water. This mixture creates a dense medium in which diamonds, due to their higher density, sink, while lighter waste material floats. This separation process requires substantial volumes of water to maintain the slurry and ensure the effective recovery of diamonds.

Finally, sorting the diamonds from the ore involves further washing and screening processes, which continue to demand significant water usage. Throughout these stages, efficient water management is critical to minimize environmental impact, reduce operational costs, and ensure a sustainable supply of water for ongoing operations.

While diamond processing does require a significant amount of water for specific stages, it generally uses less water compared to the processing of other minerals like gold or copper. This is because the main water-intensive processes in diamond mining are focused on washing and cleaning rather than chemical processing. In diamond processing, water is primarily used for washing the ore during the initial stages of crushing, scrubbing, and screening. These processes help remove clay, soil, and other impurities from the diamond-bearing ore. The water used in these steps becomes contaminated mainly with particulate fines, which are small particles of rock and soil.

Unlike other mineral processing methods, diamond processing does not typically involve the use of large volumes of water for chemical treatments, such as cyanidation in gold processing, which requires vast amounts of water to dissolve and recover gold. Instead, the focus in diamond processing is on physical separation techniques, such as dense media separation (DMS) and X-ray sorting, which are less water-intensive. In DMS, for example, a mixture of water and dense media (like ferrosilicon) is used to create a slurry in which diamonds can be separated based on their density. While this process does use water, the volumes required are less than those needed for the chemical leaching processes used in other types of mineral extraction.

Because the primary use of water in diamond processing is for washing, the resulting wastewater mainly contains suspended solids and particulate fines rather than dissolved chemicals or heavy metals. This makes the treatment and recycling of water in diamond processing relatively simpler and more environmentally friendly. The fines can often be settled out through sedimentation, and the water can be filtered and reused in the processing plant [26].

Coal Mining

The coal reserves of South Africa are found in the Ecca deposits, a layer of the Karoo Supergroup. These deposits are predominantly situated in the northeastern region of the country, shown in Figure 8. The coal seams are typically shallow, mostly free of faults, and gently sloping, making them conducive to open-cast and mechanized mining operations.

Figure 8: Coal mining activities in RSA, https://www.mineralscouncil.org.za/sa-mining/coal

The advent of coal mining in South Africa can be traced back to the late 19th century, coinciding with the start of gold mining on the Witwatersrand. The first significant quantities of coal were extracted from the Highveld coal field, located near the nascent Witwatersrand gold mines. However, demand for coal began to grow, slowly at first but then exponentially, as the country entered a period of industrialization during and following World War 2. This included a major program of building power stations, particularly on the Witbank and Delmas coal fields, as well as Sasol’s large coal-based synfuels and organic chemicals complex at Secunda. South Africa was building an industrial future and technical skills base firmly founded on its principal fossil-fuel resource. Searches for other fossil fuels to date have not been successful, and the country’s fossil future remains firmly grounded in coal.

For many years, the coal sector remained in the hands of local private entities, largely those of the old mining houses. However, particularly during the oil crises of the 1970s, foreign oil companies vied for coal resources and established new collieries, primarily to serve export markets. The Richards Bay Coal Terminal (RBCT) was established in 1976 as a partnership between the then-leading coal companies, with an initial annual capacity of 12 Mt. This capacity has steadily increased, with a fine balancing of rail capacity needed to carry coal from the inland collieries to the coast, to its current 91Mt design capacity.

As this export capacity was being expanded, seaborne coal prices were generally greater than domestic prices for many years. Consequently, there was considerable competition for capacity at the RBCT and the rail line that serves it. However, the commodities slump of the past few years and the glut of bulk commodities on international markets have resulted in export prices falling by more than half since 2013, as exporters from competing countries struggled to maintain their market shares.

Coal mining is essential for South Africa’s energy needs but can be water-intensive. Surface mining methods like open-pit mining require water for dust suppression, equipment cooling, and coal-washing processes. Coal beneficiation involves water-intensive processes to remove impurities, necessitating careful water management strategies.

Iron Ore Mining

Iron ore mining in South Africa is characterized by extracting hematite and magnetite ores, which are processed through water-intensive methods such as beneficiation and pelletization. Iron is widespread in various geological formations due to its propensity to chemically combine with other elements in diverse physical and chemical environments. Among the numerous iron-bearing minerals, only a few, including hematite and magnetite, are economically viable sources of iron.

Types of Iron Ore Deposits in South Africa

The primary types of iron ore deposits in South Africa include the following groups, and are depicted in Figure 9.

Banded Cherty Iron Formation (Algoma Type): These deposits are found in the Archaean greenstone belts and are characterized by layers of iron-rich chert.
Banded Cherty, Oolitic, or Massive Iron Ore (Lake Superior Type): This includes the high-grade deposits at Thabazimbi and Sishen, some of the country’s richest iron ore reserves.
Oolitic Hematite Iron Silicate Ore (Clinton Type): Large deposits of this type are found in the Pretoria Group of the Transvaal Sequence.
Iron Ore Deposits of Magmatic Origin: These occur in regions like the Bushveld Complex.
Small Isolated ‘Blackband’ Deposits: These are found within the Karoo Sequence.

Figure 9: Simplified geological map of RSA and locations of iron mining activities, [27]

Major Iron Ore Reserves

The largest reserves of high-grade iron ore (containing more than 60% iron) are located in the Sishen-Postmasburg and Thabazimbi areas. These deposits have been formed through the secondary enrichment of banded ironstones and ferruginous shales.

Sishen Mine Operations

Sishen Mine, the largest iron mine in South Africa, is one of the world’s largest open-pit mines. With an annual capacity of 22.5 million tons of run-of-mine ore and 18 million tons of product, the mine plays a crucial role in both local and international iron ore supply. The operation includes a planned stripping ratio of 2.5:1 (ore waste), and significant infrastructure supports the transport of iron ore, including a dedicated railway to Saldanha Bay for export.

Processing Plants

The first ore-handling plant at Sishen, commissioned in 1953, was a dry-crushing and screening facility. A wet-screening plant later replaced this in 1961, enhancing the ability to process high-grade laminated ore interbedded with shales. In the 1970s, the capacity of these plants was significantly expanded to meet growing demand, with the North Plant specifically designed for export production, achieving an annual capacity of 18 million tons.

Mining Methods

Conventional open-pit mining methods are employed at Sishen, involving drilling (with large rotary drills), blasting, and using shovels and trucks to transport material. The mine faces varying rock hardness, with some areas containing very hard conglomeratic ore, resulting in high drilling costs and lower penetration rates. In contrast, softer formations like calcrete and shale allow for higher penetration rates and lower drilling costs.

The hematite ore at Sishen occurs in beds of varying thicknesses and grades, with interbedded impurities such as shales present in the laminated ores. To ensure the supply of a product with consistent and acceptable quality to blast furnaces, either selective mining methods are employed or the ore undergoes upgrading. Heavy-medium separation can significantly increase the ore reserves by better-utilizing medium- and lower-grade ores. Therefore, a mixture of high-, medium-, and lower-grade ores is fed to the plant, where waste material is effectively separated from the ore.

Ore Quality and Beneficiation

Blast furnace performance is negatively impacted by fluctuations in the iron content of the ore. Controlling these fluctuations would be very challenging without beneficiation and the associated blending processes. The Sishen plant is specifically designed to process 22.5 million tons of raw ore per annum into three distinct products: lumpy ore between 25 and 8 mm, lumpy ore between 11 and 5 mm (direct-reduction ore), and fine ore less than 5 mm, achieving a mass recovery of approximately 80%. The raw ore, with an iron content of 57 to 60%, is upgraded to more than 66% iron in the lumpy ore and more than 65% iron in the fine ore.

Plant Operations and Maintenance

The plant operates continuously for 24 hours a day, six days a week, with a designed throughput of 4.5 kilotons per hour. Scheduled preventive maintenance is performed on various plant sections to ensure smooth and uninterrupted operations. The final products are obtained through multiple stages of crushing, wet and dry screening, heavy-medium separation, and blending.

Processing Techniques

Iron ore processing and beneficiation in South Africa involve several methods to improve the Fe content and reduce gangue content. Gangue refers to the non-valuable minerals or materials that are found in an ore deposit along with the valuable minerals or metals that are being mined. These materials are typically considered waste and are separated from the ore during the beneficiation process to improve the quality of the extracted minerals. The presence of gangue minerals makes extracting and processing valuable minerals more challenging and costly. Common gangue minerals include silica (quartz), alumina (clay minerals), and phosphorus-bearing minerals.

Techniques such as washing, jigging, magnetic separation, gravity separation, and flotation are used in different combinations depending on the nature of the ore and the impurities present. These processes aim to develop a cost-effective flow sheet that incorporates necessary crushing, grinding, screening, and beneficiation techniques to upgrade the quality of the iron ore.

The beneficiation process involves several stages. The ore is first deposited longitudinally on beds using stackers. A drum-type reclaimer is then used to recover the ore transversally. This method of stacking and reclaiming ensures that any variations in ore quality within the beds are eliminated, resulting in a uniform product quality.

Heavy-Medium Separation

Heavy-medium separation plays a crucial role in upgrading the ore. By using this technique, the plant can effectively separate waste material from the ore, thereby enhancing the quality and increasing the reserves of usable ore. This process is vital for ensuring that the final products meet the required iron content specifications for blast furnace operations and other industrial applications.

Scrubbing

Scrubbing is an essential process where water is used to remove clays, slimes, and oxidized materials from the ore. This method is primitive yet widely used in processing lumpy iron ore to dislodge and remove friable and soft lateritic materials, fine materials, and limonitic clay particles adhering to the ore. Wet scrubbing is particularly useful for hard and porous ores that have cavities or pores filled with clayey material. After scrubbing, the ore undergoes crushing and grinding.

Crushing, Grinding, and Screening

The primary goal of crushing, grinding, and screening is to reduce the ore size to liberate and recover valuable minerals. Crushing reduces the size of the ore to coarse particles, typically coarser than 5 mm, and can involve several stages depending on the ore characteristics. This can include primary crushing at the mine site and further crushing stages at the steel plant. Various crushers such as jaw, gyratory, cone, and roll crushers are used in these stages.

Grinding further reduces the ore size and can involve semi-autogenous grinding (SAG) and autogenous grinding (AG) circuits, as well as rod mills and ball mills. Closed circuit grinding minimizes over-grinding of friable ores by recirculating coarse particles back to the mill.

Screening is crucial for dry beneficiation of iron ore. It separates the ore into different size fractions, allowing for further classification and grading. Wet screening can be employed, using high-pressure water jets over screens to classify fines and deslime ultra-fines via hydro-cyclones. This mechanical separation helps produce an enriched ore containing most of the ore minerals and a tailing containing the bulk of the gangue minerals.

Beneficiation Techniques

Several beneficiation techniques are used to upgrade the quality of the iron ore:

Washing: Water is used to remove impurities and improve ore quality.
Jigging: A gravity separation technique that uses water to separate lighter gangue from heavier ore particles.
Magnetic Separation: Uses magnetic properties to separate iron-rich ore from non-magnetic gangue.
Flotation: Water and chemical reagents are used to separate iron ore particles from impurities.

Water Use in Processing

Water plays a critical role in the processing and beneficiation of iron ore:

Scrubbing: Utilizes water to remove clays and slimes from the ore.
Wet Screening: Employs high-pressure water jets for ore classification and desliming.
Beneficiation Methods: Various techniques, including washing, jigging, and flotation, require substantial water use to separate valuable minerals from gangue.

Environmental and Economic Considerations

Efficient water management is crucial due to the water-intensive nature of iron ore processing and the water scarcity in South Africa. Recycling and reusing water within the plant, implementing sedimentation and filtration systems for wastewater treatment, and using advanced technologies to minimize water consumption are essential strategies. These practices help reduce the environmental impact of mining operations and ensure sustainable water use.

Groundwater plays a crucial role in open-pit iron ore mining and processing plants, impacting both the extraction process and environmental management. The interaction with groundwater occurs primarily in two ways: managing inflows into the pits and utilizing groundwater for processing activities. Here’s an elaboration on both aspects:

Groundwater Management in Open-Pit Mines

Open-pit mines often intersect aquifers or other groundwater systems, leading to water inflow into the pit. This groundwater needs to be managed to ensure safe and efficient mining operations. Dewatering systems are employed to lower the water table around the mine, minimizing the inflow of groundwater. Pumping wells are installed around the pit’s perimeter to intercept groundwater before it enters the mine. Conversely, sumps and pumps are located within the pit to collect and remove water that accumulates from seepage and precipitation.

Controlling groundwater is essential to prevent slope instability and to maintain dry working conditions. Techniques used include:

Grouting: Injecting grout into the ground to block water pathways.
Cutoff Walls: Constructing barriers to restrict groundwater flow into the pit.
Drainage Systems: Installing horizontal drains to direct groundwater away from critical areas.

Groundwater can be a valuable source of water for various ore processing activities. Water is used to control dust and to wash the ore during the crushing and grinding steps in beneficiation. During scrubbing and washing, groundwater helps remove clays, slimes, and other impurities from the ore. The beneficiation methods discussed above, such as jigging, magnetic separation, gravity separation, and flotation, often require large amounts of water to separate valuable minerals from the gangue.

Processing plants often implement water recycling and reuse systems to mitigate the environmental impact and address water scarcity. This involves:

Sedimentation Tanks: Settling tanks allow particulate matter to settle out of the water, which can then be reused.
Filtration Systems: Removing impurities from the water so it can be reintroduced into the processing circuit.
Closed-loop Systems: Designing processing systems that minimize water loss and maximize reuse.

Challenges and Solutions

South Africa’s mining industry’s water demands pose challenges in regions with limited water resources. Competition for water with other sectors, as shown in Figure 10, necessitates sustainable water management practices.

Figure 10: Water use by sector in RSA, [28].

While mining and industrial activities are only responsible for about 5% (921 million kl) of the annual water usage, their supplies are typically from municipal networks, putting them in direct competition with potable water demand. Furthermore, the Department of Water and Sanitation (DWS) of South Africa estimates that there will be a national annual shortage in the freshwater supply of around -10%, or 1633 million kl, by 2030, meaning that mining and industrial operations will be put under increasing pressure during periods of drought. This means that mining companies are increasingly adopting water recycling technologies, optimizing processes, and engaging in community initiatives to reduce water consumption and environmental impact.

Beyond the demand placed by mining on water resources, the potential impact of such activities on the quality of natural water sources is another challenge. Gold mining has been a significant activity in the Witwatersrand area of Gauteng since 1886, particularly in the three underground mining basins of the East, Central, and West Rand. Over 120 mines were sunk in these regions, necessitating dewatering to ensure safe mining conditions. As these mines were depleted and abandoned, the mine voids, comprising tunnels, drives, and shafts, began to fill with water, leading to the generation of Acid Mine Drainage (AMD) when sulphide-bearing minerals come into contact with oxygen and water. The overflow of AMD from these mines severely threatens humans and the environment, impacting a substantial portion of the Vaal River System.

Recognizing the gravity of the situation for South Africa, the Department of Water and Sanitation (DWS) spearheaded initial short-term interventions to safeguard the environment. Efforts have been made to explore the possibility of transforming this pollution issue into a potential water source, with feasibility studies conducted at this stage. The feasibility assessment revealed the potential to treat approximately 54.8 million cubic meters of water annually to potable standards or for industrial use in the Witwatersrand region.

Additionally, reusing municipal wastewater sources can be a potential additional supply source for appropriate water uses at mineral mining and processing facilities. Numerous successful initiatives involving reusing treated municipal wastewater for industrial purposes are currently operational in South Africa. On a river system scale, return flows are estimated to contribute to 13% of the total available water. At the municipal wastewater treatment facility level, the country’s 1,150 treatment plants discharge approximately 2,100 million cubic meters of treated effluent back into the river systems annually.

The DWS is tasked with formulating guidelines for executing water reuse projects. These guidelines are essential to facilitate informed decision-making and effective implementation. They are designed to cover aspects such as management and control, project execution, technology selection, operations and maintenance, project financing, tariff development and implementation, and public and stakeholder education, engagement, and consultation across various types of water reuse projects. While the onus might rest on the DWS to initiate the treatment of municipal wastewater to reuse quality standards, mines can play an important role by assessing their water needs and categorizing them according to the particular use-cases quality requirements. This can then be matched to nearby wastewater reclamation plants’ capacities and qualities, thereby reducing the demand for potable water supply for industrial (non-potable) applications at the mining operations.

Therefore, understanding the water requirements for different minerals mined in South Africa is crucial for sustainable mining practices. Effective water management is essential to mitigate environmental impacts, comply with regulations, and ensure the long-term viability of mining operations. By embracing innovative water-saving and treatment technologies and fostering collaboration with stakeholders, the mining industry can responsibly navigate water challenges while harnessing the country’s mineral wealth. The following articles in this series will focus on the various technologies available for water treatment and conditioning and highlight their applicability to the different water demands by mining operations.

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