Case study: Pumps prove vital to decarbonisation and environmental materials

South Crofty tin mine in Cornwall ceased in 1998 but now Cornish Metals aims to reinstate production by 2026.

Tin is vital to decarbonisation and the energy transition due to its use in (soldering on) printed circuit boards, semiconductors, solar PV and is contained in both lead-acid and lithium-ion batteries.

The International Tin Association claims the world will need another 50,000 tonnes of tin per year by 2030 to meet a surge in demand. South Crofty has the fourth highest grade tin mineral resource globally, according to Cornish Metals, and the mining site is strategically well positioned as currently there is no primary tin production in either Europe or North America.

First, though the firm has had to dewater the flooded mine and treat eight million cubic metres (m³) of contaminated water so that it meets standards set by the Environment Agency. The treated, clean water can be then discharged into the nearby Red River at a rate of up to 25,000m³/day (882, 866 cubic feet).

As part of the process, eight Bredel 40 hose pumps are used for transferring sludge, while three Qdos chemical metering and dosing pumps are dosing hydrogen peroxide to oxidise the contaminated metals in the mine water. The dewatering project, with pumps supplied by locally-based Watson-Marlow Fluid Technology Solutions, is expected to take 18 months.

Bredel hose pumps have the advantage of accommodating continuous flow rates up to 108 m³/hr and are extremely durable (pressures up to 16 bar). There are no internal universal joints, valves, dead corners or glands to impact flow, and they are reversible for back-flushing. And they can handle undiluted mine water, tailings and thickener underflow with up to 80% solids.

The products are virtually maintenance-free, claims WMFTG as there are no impellers, liners or mechanical seals to replace, no check valves to clog and no rotors or stators to wear out. The only wear-part is the hose, which can be replaced in a matter of minutes with no special tools.

Qdos pumps, also low maintenance, offer accurate, linear and repeatable chemical metering across all process conditions. Chemical costs can be reduced by higher accuracy metering, with flow rates that remain constant from 0.1 to 2000 mL/min at up to 7 bar.

Qdos pumps dose hydrogen peroxide during the cleaning of the contaminated mine water, to oxidise the metals and cause iron and arsenic to precipitate out of the solution, in the first of five process steps at the WTP.

Bredel hose pumps provide the process with reliable, low maintenance and contained transfer of thick sludge - containing contaminants such as iron, manganese and arsenic - which is separated from the treated water in stages two and four. The Bredel pumps are transfer sludge out from the lamella clarifier into a tank, then pumping the thickened sludge to another tank from where it is transported to a nearby site for underground storage.

Steven Kingstone, South Crofty Project Manager at Cornish Metals, explained the pumps contributed to the water treatment plant’s goal of minimising South Crofty’s impact on the local environment. Previously the Red River received untreated mine water as a legacy of past mining activities. Water discharged from South Crofty also powers a hydro-turbine that generates up to 15% of the power consumed by the WTP.