“Virtual Curtain” Water Treatment
One of the key water related aspects of many projects is how to manage waste water. This might include the disposal of abstracted groundwater as a result of mine dewatering or yield from unconventional resource projects (coal seam gas, shale gas etc.) or waste water streams from mineral processing or other industrial activities. Often the quality of these waters is such that extensive treatment is required to enable environmentally safe disposal or reuse, so it is important that a range of treatments are considered early on to ensure that the most appropriate, and cost effective option is implemented. The benefits of thinking about waste water management as part of the overall water management approach for the project (taking a holistic approach) are more than just environmental, there can also be considerable financial benefits. This is particularly the case in areas with water scarcity (i.e. arid areas or areas with high competition for water) where the costs of water supply can be considerable (often prohibitive), and the ability to reuse/recycle water can increase the viability of the project – so long as the costs of treatment are not prohibitive in themselves. Virtual Curtain Ltd and the CSIRO have been collaborating for more than 6 years to develop long term solutions for the remediation and neutralisation of above and below surface acidic and contaminated geologically-complex wastewaters from mining and industry to tolerances suitable for discharge to the natural environment or recycling/reuse. The treatment involves the application of hydrotalcites (a layered double hydroxide mineral, primarily composed of magnesium and aluminium) suitable for:
- In situ, one off treatment of large contaminated pit lakes;
- Batch treatment of contaminated open pit lakes using satellite pits or other storage alternatives;
- In circuit treatment and remediation of process plant waste water; and
- Sub-surface treatment of contaminated aquifers by injecting a “virtual curtain” of reagents to interact with and neutralise contaminant plumes.
The potential applications are extensive, including mining, oil and gas (particularly unconventional resource developments) and other industrial ventures at all stages of development from commission through to operation and closure. It is a broad spectrum technique to neutralise acidic wastewater and remove a range of deleterious contaminants including uranium and other radionuclides. Hydrotalcites are a magnesium-aluminium sub class of layered double hydroxide mineral which is both naturally occurring and synthetically produced, with a structure that is in the form of positively charged mixed metal hydroxide layers separated by interlayers that contain water + exchangeable anions. The minerals have the capacity to simultaneously remove a broad suite of cationic and anionic contaminants via co-precipitation during and after formation. The benefits of the Virtual Curtain technology over traditional lime based treatment methods to treat acidic and contaminated waste water include:
- The treatment is typically a one-step process with simultaneous removal of anions and cations;
- Significantly reduced sludge volumes that with traditional lime based treatment methods (up to 90% less). This is particularly valuable in cases where sludge management/disposal options are limited or where the sludge may contain certain harmful contaminants such as radioactive material;
- Additives can be dissolved for solution-solution mixing with rapid reaction kinetics (less than one minute to form) and rapid dewatering;
- Hydrotalcites form and approximately pH6 or greater, settle rapidly and can easily be removed using centrifugation meaning no additional treatment for effective dewatering (as can be the case with traditional lime based precipitated sludges);
- Hydrotalcite precipitates encapsulate high concentrations of uranium, rare earth elements, copper and other valuable metals (200-500 times enrichment) which can be reprocessed (or sold to third parties for processing) to offset remediation costs; and
- Hydrotalcites can be further stabilised via calcining to form spinel or silicified to produce a synthetic chloride analogue for permanent storage for a range of radionuclides liberated during or after cessation of uranium mining.
With increasingly stringent environmental conditions for project development, operation and closure, combined with the ever increasing cost of sourcing water, advanced water treatment options are becoming a critical part of any development which generates waste water streams. The Virtual Curtain system provides a cost effective and simple process which can be used across a wide range of applications, including:
- Management of acid drainage for operating, closing or abandoned mine sites (i.e. management of acidic dewatering yield, seepage from waste dumps, disused pits or tailings dams, etc.);
- In-situ uranium acid and alkaline leach mine sites – for example leakage from cold war era uranium/extraction bores in Europe and the US;
- Management of oil and gas field brines and contaminated water, including the management of formation water yielded during coal seam or shale gas operations.
The Virtual Curtain method can also be used as a pre-treatment to reverse osmosis (RO) in areas of environmental sensitivity by rapidly removing contaminants to enhance the efficiency of the RO process. The Virtual Curtain water treatment process, whilst new, has been successful in a range of trials and full scale commercial applications, including:
- Treatment of acid leach uranium mine process water in a hard rock open pit setting;
- A sediment hosted uranium mine barren lixiviant (removed 92-99% of U series radionuclides);
- Treatment of pit lake water at two copper mines and one gold mine;
- Study trials in several uranium, rare earth and copper mines and oil field developments contaminated groundwater and process water stream management challenges.
The Virtual Curtain water treatment process is just one of an increasing range of treatment options, however its suitability to a broad range of applications is something which sets it apart from many other treatment processes available. It is important however that when considering waste water treatment options, that it is done so in line with the broader water management requirements and objectives of the specific project to optimise the entire water cycle. Contact Global Hydro to discuss all of your water management requirements. Global Hydro – “Ensuring project success through effective, responsible water management.”
About the author Ashley is a hydrogeologist and water management professional, with experience in Australia, Mongolia, Kazakhstan and China and is a member of the International Association of Hydrogeologists. Ashley started his professional career with the West Australian Government – Department of Water, using regulatory processes and tools in relation to water management for mining and mining related infrastructure projects (railways, roads, ports etc.). Since joining the consulting world Ashley has conducted and managed a range of hydrogeological, groundwater management, and multi-disciplinary (integrated ground and surface water) projects in Australia, Mongolia and Kazakhstan for a range of purposes including water supply, water management and water source protection.