This study is based on a waste management company that operates a hazardous waste landfill site and has a challenge with the production of leachate. Leachate is produced when water percolates through the waste disposal site, accumulating the contaminants, which creates the highly concentrated hazardous liquid. This leachate must be effectively treated by concentration and solidification, and accommodate larger volume increases as the landfill capacity increases. The main aim of this study was to develop a practical, feasible and economically viable technology to solidify the concentrated leachate from the effluent treatment plant, comprising approximately 8750 m³ per annum.

A 300 L/h cooling demonstration plant was developed which consisted of various equipment for freeze crystallization method such as the chiller, secondary refrigerant mixture (40% ethylene glycol, in water), clarifier, reactor and pumps. The following samples were collected at the waste management company to be used at the demonstration plant: (i) 1000 L concentrate after evaporation, (ii) 2000 L leachate (feed to the evaporator). This demonstration plant was developed with the aim of recovering clean water and Na₂SO₄ through ice formation.

OLI software simulations were used to predict the amount of salt and ice that should be recovered. The predicted results were confirmed by actual runs on the demonstration plant. Salt production was monitored over time when 302 L of concentrate was recycled. A mass of 102.9 kg of salt (Na₂SO₄.10H₂O) was recovered over a period of 6 hours, which amounts to 339.8 g/L (as Na₂SO₄.10H₂O). This corresponds well with the OLI prediction of 353.9 g/L. Ice production was monitored over time when 273 L of leachate was recycled. A mass of 118.7 kg ice was removed over a period of 5.5 hours, with the ice purity having 4.0 g/L TDS, which is substantially lower than the 46.0 g/L TDS of the feed. Energy consumption amounted to 171 kWh/ton ice, which compares well with the theoretical value of 91 kWh/ton ice for a COP of 1.

This study proved that pipe freeze crystallization is a low cost method for treating leachate. To put it in context, the total cost of waste transportation and disposal amounts to ZAR2 500/m³, while freeze crystallization only costs ZAR524.07/m³. Therefore, this study recommends that a freeze crystallization plant be built for the waste management company to save costs in treating the leachate and to also recover valuable resources.

Mineral development carries an increasing expectation for protection of water resources as focus on water supplies continues to grow. Integrating projections of anticipated mine water chemistry early in the mine design process—prior to when project specific data are available—provides the greatest opportunity for improving environmental outcomes at the lowest increase to overall schedule and cost.

An approach derived from behavioral economics, “Reference Class Forecasting” (RCF), is used in project management disciplines to empirically estimate costs and schedule by establishing a reference class of similar projects and adjusting based on project-specific characteristics. This paper applies RCF in a mine water quality context to identify a preliminary design basis for rock stockpiles. It requires a relatively low level of project definition and eliminates the inherent sources of optimism and misrepresentation bias present in bottom-up estimates. It was applied here to a scoping-level project to: (1) screen out constituents that are unlikely to influence design, (2) identify constituents that are likely to drive design, including a scale of the reductions required, and (3) identify constituents for which further review is necessary.

A hypothetical mine rock stockpile from a magmatic nickel-copper-PGE deposit located in a humid continental climate region was evaluated as follows: 1) a reference class of mines was identified based on shared characteristics that drive mine water chemistry (e.g., deposit model, climate); 2) a database was created of operational water quality data for the mine stockpile class containing approximately 5,700 individual records; 3) acceptance criteria were established that reflected project-specific risk tolerance and regional water quality standards; and 4) a statistical evaluation was conducted to compare observations from the reference class to the acceptance criteria. The RCF process narrowed the list of constituents of interest from an initial twenty-two to eight; three were likely to inform mine water quality design; five for which further evaluation was recommended. The remaining fourteen were unlikely to pose water quality risks for the project. An anticipated scale of required reduction was established for the eight remaining constituents of interest.

By narrowing the constituent list and identifying necessary reductions during mine scoping, projects can more fluidly integrate water management strategies into the early mine design. The broad application of this approach is limited by the availability of data to form a reference class of operational mine water chemistry; however, as existing repositories of data continue to become available, opportunities to leverage RCF may become more prevalent.

The leachate from coal waste dumps is the most polluted stream and poses significant environmental challenges. The current practice involves storing the leachate in evaporation ponds to evaporate and facilitate iron(II)-oxidation. This method is aimed at reducing the immediate environmental impact. If treated separately salt removal already take place in the pre-treatment stage. This method would enhance the effectiveness of subsequent treatment and help mitigate long-term environmental risks.

This research introduces a novel approach that utilizes evaporation to minimize leachate volume and facilitate the oxidation of Fe²⁺ to Fe³⁺. By exposing leachate to oxygen and iron-oxidizing bacteria, we achieve the necessary oxidation while simultaneously adjusting pH using Na₂CO₃/CaCO₃/Ca(OH)₂/NaOH. This method not only simplifies the treatment process but also allows for the direct recovery of magnetite from the solution. The study utilized HDPE pipes for solar heating, OLI software for vapour concentration predictions, and beaker studies to assess magnetite formation under varying conditions.

The findings reveal several key insights: solar energy effectively evaporates water; Fe²⁺ can be oxidized to Fe³⁺ to meet a 1:2 molar ratio; and both Fe(OH)₃ and Fe(OH)₂ can be precipitated using Na₂CO₃/CaCO₃ and Ca(OH)₂/NaOH, respectively. Additionally, the conversion of Fe(OH)₃/Fe(OH)₂ sludge to Fe₃O₄ occurs at 100°C, with magnetite formation happening in the presence or absence of gypsum. Notably, the settling rate of Fe₃O₄-rich sludge surpasses that of Fe(OH)₃-rich sludge, indicating improved separation characteristics.

The implications of this research are significant for the mining industry and environmental management. By optimizing AMD treatment, this innovative technology reduces energy costs associated with Fe²⁺ oxidation, allows for the feasible recovery of magnetite under varying conditions, and enhances sludge settling rates, leading to greater operational efficiency. Furthermore, the streamlined treatment process minimizes complications related to managing multiple slurries, thereby reducing post-treatment handling challenges. Future studies are recommended to explore magnetic separation techniques for efficient magnetite and gypsum separation, further contributing to sustainable practices in mining. Overall, this research presents a promising strategy for advancing AMD treatment and mitigating its environmental effects.

This article deals with the water resource legacies we in the mining realm are creating and leaving it behind in semi-arid regions and how some of these legacies are already monuments for future food security plans. In semi-arid regions water resources are often a fatal flaw to start new mining operations and therefore new resources needs to be developed, however once the mineral resources are depleted then the water resources will still be available and these remaining water resources will become an integrate part of a water/food security network for many millennia to come.

The most common water resources developed forming part of new mining projects are dams and wellfields and as a result during feasibility studies we never really considers the default water resources developed as a result mining and associated infrastructure. This is most probably as a result of the “naughty” minerals in the classroom for example gold and coal and over years created a stigma that the water resources legacies from mining is one of acid mine drainage linked with unwanted elements for example uranium. There is more water-friendly mineral resources for example the Bushveld Igneous Complex (BIC) with chrome and platinum and together with phosphate and potassium mines all creating new vast water resources that can be converted into food security options.

The water resources typically left behind range from underground mines fill with water and new modified aquifers or anthropogenetic aquifers. The case studies discussed specifically deals with the BIC and the AAs already developed, the phosphate aquifer now created in the west-coast of Southern Africa, potassium mine in Ethiopia transforming hypersaline alluvial fan aquifers in the Danikal Desert to fresh water aquifers and even how large gold TSF’s are now harvested to aggressively reuse tailings water and reduce the consumptive use of fresh water.

Finally, we take a brave step into the future and consider how salt water reclamation in greenhouse in the Nethe erlands can be combined with injection wells to harvest and clean our seepage water derived from scavenger wells at larges gold tailings facilities in South Africa.