Compliance and the unwritten rule to ‘go beyond compliance’ in the mining industry with regards to the environment is now more important than ever before.

There has been significant growth in responsible investor behaviour over the past few years, with environmental issues increasingly integrated into their investment decisions.

Responsible tailings management is one of the main areas of concern for the mining industry at present and mine operators are increasingly adopting alternative means of tailings disposal to minimise the impact of mining operations on the environment and as a means to comply with increasing regulation and legislation in this area, writes CHANTELLE KOTZE.

This article first appeared in Mining Review Africa Issue 4, 2020
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Tailings from mining operations are usually stored in large tailings dams as a slurry that contains the waste materials from the beneficiation process. This slurry includes mineral material, metals and any reagents used in the beneficiation process.

Minerals wet processing equipment manufacturer CDE head of business development for mining Adam Holland says that advancements currently taking place in minerals processing technology may in future eliminate the need for tailings dams altogether.

In the same vein, CDE, through its innovative approach to waste management, has identified ways to tailor its wet processing equipment into bespoke solutions that can help the broader mining industry.

These solutions are aimed at extracting maximum value through the retreatment of waste tailings material and transforming mine waste into saleable products, eliminating the need for settling ponds and tailings dams.

The company’s solutions can also be used to dewater tailings, enabling miners to reuse this water within the process, thereby reducing the need for top-up water.

While mining companies around the globe are still reluctant to invest in waste retreatment, CDE has taken an innovative approach to this by partnering with mining contractors.

The company can deliver a bespoke fully-functioning minerals processing solution to these mining contractors, which the contractor will manage and in turn supply the reprocessed mineral-containing material back to the mining company with a robust and proven return on investment.

CDE designed, manufactured and installed a turnkey iron ore waste beneficiation system for SIMEC Mining, comprising two CDE processing plants, in the remote Middleback Ranges of South Australia.

Commissioned in late 2017, the two CDE processing plants were capable of washing, separating and gravity beneficiating around 17 Mt of low-grade, lump overburden iron ore that was stockpiled in waste dumps, into a high-grade saleable product with a 63% iron content – upgraded from an average low-grade grade of between 45% and 50% iron content in the waste dump.

Holland says that CDE’s processing plants provide a cost effective way of extracting the best possible value from material that has already been mined as a means of adding to a company’s bottom line.

“In a boom cycle, this is the most cost-effective way of mining additional resources whereas in a bust cycle, it is a lucrative way to increase production volumes as a means to counter the loss of income from expensive primary production methods,” Holland explains.

While ore prices are holding their own in our present challenging global economic situation, it is widely predicted that prices could drop to circa US$50/t, which is a climate where the latter scenario becomes very appealing.

In a South African context, Holland believes that this lump iron ore processing technology can be applied to retreat the country’s fine iron ore tailings; for the reprocessing of tailings dams; and for the diversion of tailings from wet dams to dry stacking.

The company has found success in suppling this type of solution to mining companies in Brazil – a country that has suffered several wet tailings dam failures in the recent past.

The customised tailings management system may comprise of a variety of processing phases, including:

  • Fines management – Recover material for further use and minimise waste volumes;
  • Primary water treatment – Recover over 95% of process water for recirculation to the ore processing plant;
  • Final tailings dewatering – Through dewatering and dry stacking and production of cake with dry solids content of 80%, effectively eliminating the requirement for tailings dams;
  • Mineral flexibility – CDE’s systems can be applied in the processing of a variety of ores, including gold, copper, zinc, and iron ore.

Holland believes that this combination of processes is applicable in South Africa, as environmental restrictions are changing and becoming more stringent, there is increased focus on making tailings dams safer and more sustainable.  

In addition, miners are cognisant that there is valuable ore to be gained from their tailings dams and stockpiles, and there are by-products including sand and grits that can be used in the construction industry or for ground remediation, while the finer material that is dewatered can be used in road brick manufacture, from which revenue can realised.

Other benefits include environmental improvements and a significant reduction in health and safety risks to on-site personnel and neighbouring communities.

Water recovery and recycling

In remote or arid areas with limited water availability (making wet processing almost impossible), CDE’s thickener technology can be used in a number of different commodities and can enable a new plant to proceed as a result of the significant reduction in the volume of fresh water required to feed the washing plant.

The thickener separates the suspended solids from the hydrocyclone overflow with the addition of a flocculent. This allows the solids to sink to the bottom of the thickener tank, while the clean water overflows a circumferential weir and is recirculated to the washing plant.

The settled sludge is then pumped away from the thickener where it can be sent to a filter press or centrifuge, which produces a dried filter cake with +80% dry solids content, and where further water is recovered.

The thickener is able to recover up over 90% of the water, reducing the top-up water to less than 10% of the plant throughput, combined with filter press or centrifuge technology, water recovery can be further increased to 95%.

In addition to this, water can be recovered from stockpile material through stockpile underflow vacuum systems, which could increase total water recovery to above 95%, notes Holland.

Delivering a solution of the future NOW

CDE recently launched what it deems the ‘solution of the future’ – the 500 tph Combo X900 – an “all-in-one wet processing and water management solution for fine ores”.

Holland notes that while the Combo X900, and smaller Combo X400, were originally designed to process natural sand and crushed rock, containing unwanted clay, silt and other organic contaminants and extract washed sand products, the Combo is equally effected for tailings recovery, dewatering, dry stockpiling and sludge management.

The Combo X900 combines all essential processes – washing, dewatering, water recycling, and stockpiling – onto one single, interconnected and pre-assembled plug-and-play system.

The small footprint machine is highly applicable to the African market for tailings recovery. The machine, which can be deployed in less than a week due to its modular nature, is movable and can be broken down, moved from one tailings dam to the next, and be rebuilt in a very short space of time.

Listen: Investing in safe & sustainable tailings management

CDE’s range of flexible and modular plant solutions, including the Combo range, could be a game-changer in addressing the tailings management challenges faced by the African mining market, Holland concludes.