Golder talks diverse water solutions

Ahead of the Water Management article in the March issue of International Mining, Golder Associates reports on several cutting-edge mine water reclamation and reuse projects in which it has been involved. One such example is a South African project for Optimum Coal where reclaimed mine water was converted into a clean supply of drinking water for communities in neighbouring areas. For this project, Golder designed and engineered the entire water management system, and secured all regulatory approvals, including the Environmental Impact Assessments. Andre Van Niekerk, Principal Water Engineer comments: “A major challenge here was that the designs had to consider various aspects, such as geological formations, existing services, proximity to existing and future mining, and the presence of local settlements.

“Another big challenge was that the Golder team had to negotiate the project authorisations with four different regulatory authorities. Despite the challenges presented during the project, the mine water reclamation for Optimum Coal was very successful.

In general, Golder helps mining operations to recycle and reuse return water from the tailings, and from waste disposal and storage facilities. It’s common for modern mines to capture impacted mine water for reclamation and reuse within the mining operations, minerals processes operations, and waste handling and disposal operations. The main advantages of this are that it reduces the freshwater intake to the mining operations and that it reduces the discharge of impacted mine water.”

He adds: “In addition to the South African project for Optimum Coal, Golder has been involved in a wide range of other complex water management projects, which have incorporated water recycling, desalination and tailings. When recycling mine wastewater for mineral processing, it is important consider the volumetric aspect. In other words, there must be sufficient levels of water available to satisfy the different mineral processes. It is, therefore, vital to understand the integrated water balance of a mine before proceeding with specific water recycling and reuse activities. In general, for reclaimed water to be fed back into the processing lines at mines, it needs to have a near neutral pH and a low potential for precipitation of nuisance compounds, such as gypsum. This can typically be achieved by lime and limestone treatment, gypsum crystallisation and clarification to remove suspended solids.”

Golder regularly uses a diverse range of mine water treatment technologies. These can be broadly classified in terms of the pollutants contained with the impacted mine water. For acidic/low pH water, the use of lime and limestone, as well as other alkaline solutions, is common. Constructed wetlands are often a good way of introducing alkalinity into mine water. For water with heavy metals, such as iron, aluminium and manganese, lime and limestone treatments are also common. Essential here is the creation of a biological sulphate reduction that allows for sulphide precipitation within the minerals. Once again, constructed wetlands are often used to achieve this.

“For water with high salinity, our recommended methods of treatment would include membrane-based nanofiltration and reverse osmosis, ionexchange technologies, and certain precipitation technologies for sulphate removal – such as using the sulphate mineral ettringite. Golder regularly works with all of these methods in projects across the globe.”

On water sourcing trends, he told IM: “Over the last five or ten years, water in mining has become an increasingly important area of focus and is driven by changing legislation and climatic conditions. In water scarce locations, reusing water has become essential in making mining operations efficient. This is particularly relevant in areas such as southern Africa and the west coast of South America. Additionally, many regions that are less water scarce have also put great emphasis on recycling water. Several of these, such as Sweden and the UK, are driven by regulatory policies and country-specific legislation. In the future, competition for scarce water resources in mining areas will lead to increased competition in the impacted water recycling sector. This is compounded by local regulatory pressures, global expectations on conducting sustainable mining, and increased calls for responsible use of limited resources.”