The repair and expansion of the Spence Copper Mine tailings dam in Northern Chile was completed in December 2021. The Penetron System provided a crucial – and permanent – waterproofing solution for the large dam, a 2,855 ha (7,050 acres) storage area for toxic mining waste.
Located in the Sierra Gorda district of Northern Chile, the Spence open cut copper mine is owned and operated by BHP, one of the world’s largest mining companies. The company recently completed the Spence Growth Option (SGO) project to extend the useful life of the Spence copper mine by more than 50 years. Centerpiece of the SGO project is a $2.46 billion concentrator plant that processes minerals from the mine by conventional flotation methods to produce copper and molybdenum concentrate. The new plant can process 95,000 tons of raw material daily, producing an annual output of 185,000 tons of copper (in concentrate) over the first 10 years of operation.
A crucial part of the SGO project was the repair and expansion of the Spence mine tailings dam, an earth-fill embankment dam used to store the mining waste that remains after separating the copper ore from the gangue (material that surrounds, or is mixed with, a mineral in an ore deposit). Tailings, or rock already stripped of valuable minerals, stored in a dam can be liquid, solid, or a slurry of fine particles. They are usually highly toxic and potentially radioactive.
Permanent Solution Needed
“Unlike the more familiar hydroelectric dams, a tailings dam is designed for permanent containment; once deposited in the dam, the material stays there forever,” explains Domingo Lema, Managing Director of Penetron Chile. “This type of long-term containment poses unique challenges to the reinforced concrete structure lining the dam.”
A construction consortium – encompassing Emexco SA and Conpax – was put in charge of the $170 million project in Calama, Chile. However, the original project specifications had no plans for concrete waterproofing.
Repairing the Damage
The Emexco engineers contacted Penetron Chile for help when numerous leaks appeared in the existing reinforced concrete structures after exposure to the aggressive tailings from the mine.
As a first step, the Penetron team recommended cleaning out and filling all the existing leaks with PENECRETE MORTAR, a crystalline mortar used to repair cracks, form-tie holes, honeycombed areas, and structurally damaged concrete. The next step was a applying a layer of PENETRON, a topically applied, integral crystalline waterproofing material, to waterproof the entire concrete surface – the bottom slab and perimeter slopes of the dam. PENETRON ADMIX was added to the concrete mix for the new construction to ensure a durable and waterproof structure from the start.
For the tailings dam, PENECRETE MORTAR sealed 60 m (200 feet) of cracks; PENETRON was applied to almost 5,000 m2 (5,980 yd2) of concrete surfaces; and Petreos, the ready-mix concrete supplier, treated about 10,000 m3 (13,000 yd3) of concrete mix with PENETRON ADMIX.
Keeping Toxic Waste Contained
Once added to the concrete as an admixture or applied to a prepared concrete surface, the proprietary chemicals in all Penetron crystalline products react in a catalytic reaction with moisture to generate a non-soluble crystalline formation throughout the pores and capillary tracts of the concrete. This formation permanently seals micro-cracks, pores, and capillaries against penetration of the liquid toxic waste in the Spence Mine tailing dam. The non-soluble crystalline formation generated by Penetron crystalline materials becomes an integral part of the concrete matrix and performs consistently during the service life of the concrete.
“The Penetron System was chosen for the tailings dam thanks to ease of application and a reliable guarantee of permeability reduction and continuous self-healing of cracks,” concludes Domingo Lema.
Getting started: The repair and expansion of the Spence mine tailings dam in Chile started with a protective layer of concrete to protect the earth-fill embankment dam.
Pouring PENETRON ADMIX-treated concrete: The crystalline admixture was used to treat the new concrete segments to protect the reinforced concrete structures from the aggressive tailings from the mine.
