Mining

Acid mine drainage is characterized by pH as low as 2-3, dissolved iron concentrations up to several hundred ppm, and heavy metals including arsenic, lead, cadmium, and zinc at levels that can exceed discharge limits by orders of magnitude. Standard RO membranes are not pH-compatible with raw AMD and require upstream pH adjustment to above 6.0 before membrane treatment is feasible. AMPAC USA designs mine water treatment systems with staged chemical treatment, precipitation, and clarification before the membrane array.

Heavy metals are most cost-effectively removed by raising pH to between 8.5 and 10 with lime or caustic soda, which precipitates metals as hydroxides that can then be settled and filtered. The specific pH target varies by metal: iron precipitates near pH 7, while arsenic and cadmium require pH above 9 for effective removal. Following chemical precipitation, RO or nanofiltration provides a polishing stage to achieve discharge or reuse quality.

ZLD for mine dewatering is achievable but capital-intensive, typically using RO to concentrate reject, followed by a brine concentrator and crystallizer to produce a dry solid waste stream. The economics depend heavily on water disposal costs, regulatory pressure, and the value of recovered water for process reuse. Our project team evaluates ZLD feasibility against conventional high-recovery RO systems to help mining operators choose the approach that meets compliance requirements at the lowest lifecycle cost.

Flotation circuit water reuse requires controlling reagent carryover, particularly residual frothers and collectors that can depress recovery in subsequent flotation stages if recycled without treatment. Clarification and filtration to remove solids below 50 ppm total suspended solids is usually sufficient for coarse reuse, while RO or ultrafiltration is needed for applications sensitive to dissolved reagents. AMPAC USA sizes process water recovery systems for the high flow rates typical in large-scale mineral processing, often in the millions of GPD range.

Remote mine sites often lack reliable grid power, so our systems for mine applications are available in diesel-generator-compatible configurations and can be containerized for transport by truck or helicopter to inaccessible sites. A 50,000 GPD mine water treatment system requires approximately 30-50 kW at steady state depending on source water chemistry and treatment complexity. We design for minimal operator intervention through automated chemical dosing, remote monitoring, and alarm notification via satellite.