Maximizing Mine Impacted Water Treatment

As water scarcity continues to grow more severe and environmental water treatment regulations are in flux, it’s critical for the mining industry to implement technologies that will reduce operational cost of water treatments and meet the required environmental targets.

One of the most common, and difficult, challenges of mining water treatment is related to the treatment of sulfate-rich mining water and acid mine drainage, which is facing tightening regulation. The mining industry is required to reduce sulphate concentration below 1000 mg/L (or even below 500 mg/L), all while maintaining efficiently and high recovery. However, existing technologies used by the mining industry to accomplish this can entail high operating costs, and can also have detrimental effects such as scaling and biofouling of RO membranes.

To overcome these challenges and expand the current limits of mine impacted water treatment, the industry is seeking alternative technologies. For example, IDE's patented MAXH2O Desalter technology is a single stage reverse osmosis (RO) technology with an integrated salt precipitation unit that solves the challenges and disadvantages of existing technologies.

This technology aims to significantly reduce brine reject volumes from both industrial effluents and brackish water desalination plants, while ensuring a more robust and efficient process. This technology combines a proprietary reverse osmosis (RO) system with an integrated salt precipitation unit based on Royal HaskoningDHV (CRYSTALACTOR^TM), which may be connected to any new or existing system.

During the MAXH₂O Desalter process, mine impacted water (MIW) is cycled through the RO system at high shear velocities. This significantly reduces the salt concentration build up near the RO membrane wall, and prevents the precipitation of sparingly soluble salts and bio fouling on the membranes.

After the RO stage, MIW flows through the Crystalactor, where it reduces the saturation of sparingly soluble salts, enabling continuous cycles through the RO system until the maximal brine osmotic pressure is reached. Together with sparingly soluble salts, antiscalant that prevents scaling in the RO elements, all adsorb and precipitate on the seed particles, creating salt-coated crystals. No filter or other mechanical dewatering equipment is required. The high content of dry solids in the obtained crystals can be used for soil neutralization, road building, animals’ food additive, cement making and other applications.

MAXH₂O Desalter was successfully tested with MIW with high concentrations of sulfates. Results demonstrate a recovery rate of over 87%, and a calcium sulfate saturation index that theoretically surpasses 1,000%. In practice, the continuous precipitation of calcium sulfate in the integrated salt precipitation unit, maintained the calcium sulfate saturation index in the range of 200%- 400% during operation, protecting the membranes from scaling throughout operation.

Additionally, the system operated without the addition of chemicals other than antiscalant and calcium carbonate crystals, acting as the seeding material in the Crystalacor. Discharged pellets contain more than 90% dry solids, which means no further sludge dewatering treatment is required. Depending on the effluent requirements, the obtained RO brine stream could be further treated, e.g in a high-density sludge step, or blended with the RO product stream, pushing the total recovery rate of the system even farther to comply with environmental discharge limits.

Operational cost savings are enabled due to decreased chemical consumption and the elimination of sludge production, while competitive investment costs are made possible due to higher water recovery rates.

The ability of this technology to practically eliminate the recovery limitation of water chemistry by gradually precipitating sparingly soluble salts on pellets, while operating the RO membranes at high velocity with inherently high shear forces, allows the RO unit to meet its maximal production and recovery potential, overcome chronic RO scaling and bio-fouling issues, and drive operational efficiency.