Mining waste set to grow, but ‘reduce, reuse, recycle’ solutions abound

7th September 2018 By: Tracy Hancock - Creamer Media Contributing Editor

Mining waste set to grow, but ‘reduce, reuse, recycle’ solutions abound

The evolution of waste management techniques to accommodate the shift to low-grade ores by mining operations is one of the key emerging trends in the global mining waste management market, states UK market research company Technavio.

The London-headquartered company explains that, in the last decade, the evolution of mining procedures indicates that ore grades of most mineral commodities are on the decline, with the amount of waste generated at mining sites directly proportionate to the quality of ore grades.

The global mining waste market is thus expected to grow from the 68.76-million tons generated in 2017 to nearly 87-million tons by 2022, with 10% to 13% of the overall market contributed by South Africa, estimates Technavio.

Therefore, at most, the country can expect its mining waste to grow by about 2.36-million tons from the about 8.9-million tons it produced in 2017 to about 11.3-million tons by 2022.

Besides low-grade ores, this growth in mining waste, says Technavio’s ‘Global Mining Waste Market 2018 to 2022’ report, is the result of increased demand for mining activities to support rising urbanisation and proposed infrastructure investments to meet the needs of the world’s growing population.

The proportion of the world’s urban population is expected to increase to about 57% by 2050 from 47% in 2000, according to regional multilateral development bank African Development Bank. In the developing world, during the last two decades, Africa has experienced the highest urban growth, with the continent’s urban growth expected to hold at 3.5% a year into 2050. The bank says this will require investment in infrastructure development and the upgrading of urban settlements, and that Africa’s rapid urbanisation will place increased pressure on natural resources and the environment.

Another advancement on the horizon linked to the demand for natural resources, which Technavio says will positively impact on the market potential for mining waste management, is deep-sea mining. The world’s first deep-sea mining project owned by Canada-headquartered Nautilus Minerals is expected to kick-start in Papua New Guinea in 2019. Mining activity is also expected to be driven by the expansion of markets for mineral commodities, owing to new applications for minerals and metals, says Technavio.

With Africa hosting an array of mineral deposits, the continent is buzzing with mining and exploration project activity, and a growing number of mining companies operating on the continent.

Technavio explains that, currently, the African mining waste management market is split between a handful of companies, namely South Africa-headquartered companies EnviroServ, Interwaste, Jones & Wagener and Knight Piésold, and Ghana-based Zeal Environmental, active on the continent. “However, with strict government regulations, coupled with environment awareness, it is also possible for several small companies to enter the market in the form of independent waste management service companies.”

As low-grade ores have a low proportion of extractable minerals and metals to waste rock, which results in high energy and water consumption, generating large quantities of waste during the production process, waste management technology has evolved to suit low-grade ores.

“Advanced hydrometallurgical process and hybrid methods are being developed for the recovery of metals from low-grade and complex sources. Similarly, biopro- cessing could be combined with other hydrometallurgical unit processes to reduce waste,” says Technavio.

Contaminated water, often referred to as brine containing a high salt content, can be generated through processesing. Some remedial processes using bio- remediation of these solutions could be considered and should be implemented as a potential solution to remediate waste- water from processing, states local gold mining group Pan African Resources CEO Cobus Loots.

“The rising popularity of bio/green mining, which involves the process of using microorganisms to extract metals of economic interest from rock ores or mine waste, is another major highlight in the market that has seen significant traction in the recent past to reduce the environmental impacts associated with the extraction and processing of minerals and metals.”

In addition, Technavio tells Mining Weekly that the increased requirement for advanced, energy-efficient technologies to reduce the operating costs of waste treatment is expected to drive the adoption of membrane separation, sulphide treatment and metal recovery systems, and reduce water use and wastewater discharge.

“Further, over the forecast period, [2018 to 2022], underground mine sealing technologies are projected to develop and promote acid mine drainage treatment in closed underground mining facilities. Thus, the need for technological and process advances will fuel the growth of the global mining waste management market,” says a senior oil and gas research analyst at Technavio.

The main forms of waste produced by the mining industry remain waste rock and tailings – the fastest-growing products, says Technavio. Despite modern mining practices, the increasing rate of tailings dam failures is the main driving force behind the market share growth of tailings. The waste rock segment held the largest market share in 2017, accounting for nearly 78%. This percentage is expected to decrease by 2022, at which time tailings will account for nearly 23% of the total market share.

A continuing trend in the management of this waste is the reprocessing of waste rock and tailings to extract metals and minerals that escaped the initial mining process.

Several projects are being implemented in South Africa. The country’s latest tailings retreatment project to come on line is Pan African Resources’ R1.7-billion Elikhulu project, in Evander, Mpumalanga. The project consolidates three Evander Mines tailings dumps (Kinross, Leslie-Bracken and Winkelhaak) into one larger facility – the extended Kinross tailings facility – and is expected to process 12-million tons a year using hydraulic mining to produce 50 000 oz/y of gold for the next 14 years.

There is 200-million tons of tailings sitting on surface at Evander, which started mining in 1956. On completion, Elikhulu will have reduced Evander Mines’ environmental footprint and associated environmental impact, and will see the rehabilitation of the dump.

Officially commissioned in August, Elikhulu, says Loots, is a project that “ticks all the boxes”, delivering safe operations for staff and stakeholders, as well as sustainability in terms of cost over a long life, and serving the environmental purpose of freeing up the dumps for agricultural use, residential expansion and other developments.

Loots explains that, despite retreating historical mining waste, Elikhulu is also cognisant of reducing, reusing and recycling the waste it generates. The project is geared to reuse as much water as possible, reducing its dependence on other sources. At Elikhulu, Pan African will source water from an evaporation- controlled dam over the life of the project. Therefore, there is minimal impact on potable water. Elikhulu will use 40 Mℓ of water a day, half of which will be return water from the tailings through the tailings facility storage system.

Meanwhile, waste management companies are also using tailings as backfill in underground mines, instead of drying, stacking and storing it in openpits or pumping the dried mining waste into tailing ponds on site, says Technavio.

Global project, engineering and technical services company Wood environment and infrastructure solutions business mining VP David Bleiker states that using tailings for backfill can reduce the surface disposal of tailings by 50% and reduces the need for quarries to generate rock for structural backfill underground. “It simultaneously uses a waste material while reducing the need for additional resources.”

Further, where geochemically suitable, waste rock can be used as backfill, aggregate in road construction and landscaping material. Bleiker adds that Wood routinely looks at using mine rock for aggregate for construction on site and where feasible off-site.

Another use for waste rock is as feedstock for cement and concrete, with companies in this industry also repurposing slag, a by-product of the steel and iron industry, which is milled to a fine consistency.

With the cement industry producing 5% of global carbon dioxide (CO2) emissions, high-quality construction materials supplier AfriSam cementitious executive Hannes Meyer tells Mining Weekly that the use of granulated blast furnace slag in its cement is a strong focus for the company. The use of slag is one of the main contributors to reducing CO2 emissions for every ton of cement produced from 900 kg to 650 kg of CO2 when incorporating slag.

“Therefore, we are continuously looking for ways to increase our slag consumption. AfriSam has three projects presently running, with each at different stages (development, trials and near implementation) aimed at increasing the offtake of slag and reducing the company’s carbon footprint,” says Meyer.

AfriSam has been producing slag cement under its Slagment brand for more than 50 years, starting production in 1954. However, Meyer points out that slag in cements has been around since the 1800s.

The company can produce 800 000 t/y of slag cement at its Vanderbijlpark facility, in Gauteng, but is only using 60% of this capacity, with half this production capacity comprising slag. Therefore, AfriSam currently prevents about 400 000 t of slag from ending up in stockpiles each year.

A percentage of this slag also makes its way back to the mining industry, with AfriSam producing custom slag products: Conbex, comprising a high percentage of slag, and Fillcem, which has a higher clinker content. Conbex is a binder, generally used by the mining industry for cut-and-fill or room-and-pillar backfilling where high early strength gain is not required. Fillcem is a binder designed for use with classified or unclassified mine tailings in backfill systems in deep-level mining. Fillcem can be used on its own or with Fillgel to produce rapid gelling and stiffening of backfill slurry. Fillcem is resistant to acid mine water and is also used for the stabilisation of pillars.

Meyer believes more people should use slag cement, stating that the benefits of slag are underestimated or not well understood. He says that slag cement can double the life of buildings and is “absolutely critical” for use in coastal area construction and in underwater applications, as slag produces an alkali- resistant cement and lowers the heat of hydration during the exothermic reaction that takes place during the setting process, which can cause cracks.

Bleiker tells Mining Weekly that, while the goal is to reduce the residual waste remaining on a site, for the foreseeable future, there will be residual materials that will need to be managed on site.

Tailings and mine rock are the high-profile materials, but everything from lubricants to lunch room waste needs to be managed. “This requires safe and secure facilities that can be reliably designed, constructed, monitored and maintained. During operations, when there are numerous mine staff on site, this is relatively straightforward. However, this may be challenging once closure is reached, as there may not be any full-time staff on site. This needs to be considered at the outset when establishing and designing waste management programmes.”

Nonprofit organisation Rose Foundation CEO Bubele Nyiba tells Mining Weekly that South African mining companies are “quite good” at the safe disposal of their used oil.

“One litre of oil can contaminate one-million litres of water. If you look at the situation in the Western Cape, you will soon realise that we cannot afford to allow South Africa’s surface and underground water resources to be contaminated.”

Many of the companies accredited by the foundation collect used oil from mines, which store their used oil in bulk storage facilities between collection intervals.

There are also many drum reconditioning plants in South Africa, which produce high-quality drums that are sold back into the market, says Nyiba, pointing out the decrease in drums dumped at landfill sites as a result.

South Africa has about 200 used oil collectors, 20 transfer stations and 23 processing facilities recycling a collectable volume of about 100-million litres, as well as used oil from neighbouring countries such as Botswana and Mozambique. The country’s mining industry consumes about 25% of the lubricants sold on the local market, which equates to 300-million litres a year. Nyiba estimates that, in South Africa, the conversion rate of new oil to used oil is 40%.

The mining industry is generally not a user of the industrial fuel produced from used oil, as the sector uses sophisticated machinery that requires new lubricants. Nyiba explains that used oil is largely used as burner fuel by asphalt plants for the manufacturing of road surfacing material, kilns for brickmaking and sand drying, and lime production, as well as other industrial heating requirements.

Nyiba adds that all the used oil produced in South Africa is consumed locally, with demand exceeding supply.

Bleiker says there is no one “answer” as to the management system or the ability to reduce, reuse or recycle. “As you can imagine, the [solution] for a mining facility in close proximity to a sizeable city, and sometimes within a city, is going to be different [from that for] a remote mine with fly-in and fly-out access.”

Bleiker notes that the biggest trend in repurposing, reusing and recycling, as well as limiting, mining waste, is innovation.

“Innovation does not just happen – it means asking questions as early in the design/concept process as possible. Should we incinerate the sewage sludge to capture the heat and consume less oil or gas for heating, or is it useful as compost? The trend is . . . [to give] greater thought to waste management earlier on in the project development process.”

Bleiker says, in general, mining costs directly benefit from reduction and reuse of waste on site. At remote sites, limiting what comes on site reduces the costs involved in waste removal or management on site. The recycling and reuse of waste off-site can be challenging, as there is often considerable environmental and economic costs involved in transporting recycled goods.“Consider, for example, the fuel used to haul recycled goods from a remote mine site to recycling facilities. The fuel has an economic cost and there is an environmental cost with respect to CO2 and other emissions,” Bleiker highlights.

“In general, managing residual waste means additional risk should the management or engineered systems not work as specified. This is both a financial and an environmental risk. There is also the further cost of maintenance should the residual waste require long-term management.”

In closing, he says there is a definite advantage to increasing the three ‘Rs’, adding that mining companies are receptive to investing in effective waste management systems and programmes. “Mining companies are run by people with friends and families. No one wants to leave behind an environmental liability. Those same people are also responsible to investors, as is the case with other industries.”