Our latest case study focuses on a client of ours working in the mining industry in Mozambique in southeast Africa. This unique project involved a pontoon-mounted vertically immersed progressing cavity pump. 

This was specifically developed to maximise the effectiveness of the company’s tailings dam slime management at their mining sites.

What is tailings dam slime management and why is it important?

Dam or tailing slimes are waste material from mining. The mechanical and chemical processes involved in mining production grind the rock into a fine sand to extract the valuable mineral or metal from the rock ore. All of the unrecoverable and uneconomic remnants left over are waste and include finely-ground rock particles, chemicals, minerals and water. 

Depending on the type of mining, tailings can be liquid, solid or a slurry of fine particles. What’s more, many substances found in tailings are toxic and can contain large amounts of cyanide, mercury and arsenic, and may even be radioactive.

What are tailings dams?

Tailings dams are used to store the waste materials and water that are a by-product of the mining process. They can be as big as lakes and reach 300 metres high. As the waste slurry is piped into the dam, the solids settle to the bottom and the water is recycled to be used in the separation process again. 

Tailings dams often use earth or rock to create a barrier, and sometimes the tailings themselves are used to form the barrage. The dam is then continually raised to take in more waste and the dam becomes more unstable and prone to leakage. 

Not surprisingly, tailings dams need regular maintenance and monitoring to ensure that there is sufficient drainage and that the dam is strong enough to contain the mining waste.

What happens if the dam collapses?

In the ten years up to 2018, there were 31 recorded major tailings dam failures – and this doesn’t even include the catastrophic failure of mining company Vale’s dam in Brumadinho, Brazil on 25 January 2019, in which 300 people are believed to have lost their lives. 

In 2015, the Samarco dam collapse also in Brazil released 33 million cubic metres of iron ore tailings slurry into the environment. Considered to be the worst environmental disaster in their history, it killed 19 people, displaced 600 families and contaminated waterways for 620km downriver. 

Tailings pumping failures can also cause significant environmental and ecological damage: 

• The Jagersfontein tailings dam collapse in South Africa in September 2022, was a structural failure of a tailings dam used by a stockpile mineral re-processor. It caused a mudslide through the town and surrounding farmland 

• In Canada, the Mount Polley copper-gold mine dam collapse in 2014 released 25 million cubic metres of wastewater and tailings into adjacent water systems and lakes 

• The Ok Tedi environmental disaster caused severe harm to the environment along 1,000 km of the Ok Tedi River and the Fly River in the Western Province of Papua New Guinea between 1984 and 2013. The lives of 50,000 people have been disrupted 

• In November 2012, the Sotkamo metals mine in Finland released hundreds of thousands of cubic metres of waste water. This raised concentrations of uranium, nickel and zinc in the nearby Snow River to at least 10 times the harmful level 

• The Ajka alumina plant accident in 2010 in Hungary, released one million cubic metres of red mud, a waste product of aluminium refining, flooding the village of Kolontár and killing the Marcal River 

• The Baia Mare cyanide spill in Romania in January 2000 was called the worst environmental disaster in Europe since the Chernobyl disaster 

It’s therefore clear that tailings management through ongoing maintenance and monitoring is vitally important. It is essential that all tailings pumping equipment works as effectively as possible to prevent this kind of environmental disaster from occurring again.

So what was the problem?

Our mining client in Mozambique was having difficulty managing the existing thickened slimes within their tailings dams. 

They were using submersible centrifugal pumps which kept failing due to insufficient cooling within the dams. This is because a submersible centrifugal pump works by circulating fluid around the pump to cool the attached motor. When liquids like sludge or tailings become dense they don’t flow around the pump and create a cooling effect, which quickly leads to the pump overheating. 

Our client wanted to use a vertically-immersed positive displacement pump to discover at what density the slimes could be extracted from the settling dam. The positive displacement pump would be mounted on a pontoon and would be inclined at different angles to remove thickened slime from ponds. 

The pump had to be robust enough to withstand being mounted at various angles during operation, and strong enough to handle thickened slimes with solid concentrations up to 45%, and which can be extremely abrasive.

What was our solution? 

Here at North Ridge Pumps, we’re not tied to a single pump technology, so we can provide the best pump for a particular application and designed for the lowest lifetime cost. Indeed, we can use our expertise to offer a bespoke solution, not something which just comes off the shelf. 

For our client in Mozambique, we designed and manufactured a 5.2m progressing cavity pump from cast AISI316 stainless steel to remove the slime. Progressing cavity pumps are a type of rotary positive displacement pump where a helical shaped rotor rotates within a fixed stator. Due to its helical shape as the rotor rotates, a cavity is formed between the rotor and stator as it travels through the pump. 

The rotor within the pump operates at a slow rpm and must be lubricated by the fluid being pumped. This will ensure that it doesn’t run dry as clearances between the rotor and stator are very fine. This means that if the pump is not filled on start-up dry running can occur, causing the stator to burn and disintegrate. 

The volume of liquid pumped is proportional to speed which gives a predictable linear tailings pumping rate across a range of pressures. This technology delivers one of the highest flow and pressures available from a positive displacement pump –up to 600M³H and 48bar, with efficiency ranging from 55% to 75%. This technology is most suited to viscous, lubricating fluids between 1cSt and 1million cSt. 

Working at 130M³H up to 12 bar, the mechanical seal on our progressing cavity pump had a flushing kit to ensure the seal faces remained free from solid particles which could damage the pump. 

The pump was coupled to a 75Kw 3-phase motor suitable for inverter drive. The pump would operate at speeds as low as 125rpm ensuring that it didn’t suffer any abrasive wear. The 6” pump suction allowed soft solids up to 96mm in diameter, and hard solids up to 48mm in diameter. 

The progressing cavity pump was assembled and despatched in under 16 weeks, and met all of the tailings management requirements and specifics our Mozambican client had required. If you have an application involving the transfer, circulation or injection of viscous solid-laden liquids and are unsure of which pump to use, speak to North Ridge Pumps to see how we can help.