Demonstration of a high-throughput treatability technique for evaluating the physico-chemical treatment of wastewater and tailings
The treatment of wastewater has become a significant financial and operational challenge for many mining and industrial sites globally. Efficient and sustainable water usage is fundamental for all water-based operations to maintain a social license to operate. In the mining industry, ore processing is water intensive. The recovery of water used for ore processing is essential to mining operations, especially in arid climates with scarce water sources (Chambers et al. 2003, Wels & Robertson 2003). Industrial processes, such as pigment production and petrochemical refining, also require large volumes of water. Like the mining industry, these applications also strive for efficient water usage.
Many wastewater treatment plants involve the use of physico-chemical processes such as coagulation, flocculation, clarification, and filtration to separate waste solids from a liquid or slurry stream. A key step in physico-chemical water treatment processes is bench-scale testing to optimize the addition of chemical coagulants and/or flocculants. The conventional strategy is to use the standard ‘jar test’ method. There are numerous examples where jar testing has been used in mining and other industries to evaluate the performance of coagulants and flocculants (Sabah & Cengiz 2003, Gnandi et al. 2005, Yang et al. 2010, Ebeling et al. 2003, Ebeling et al. 2005). Jar tests are sufficient to evaluate the performance of a small number of chemicals when precedent exists for treating a particular water stream. Each individual ‘jar test’ requires relatively large volumes (1 to 2 L) of sample, therefore limiting the number of tests that can be performed in a reasonable amount of time for a given water sample.
When no precedent exists for a treatment protocol, such as for complex mine waters, the conventional jar testing method does not allow for various chemical coagulants and/or flocculants to be tested in a cost-effective manner. In order to test a wide range of chemical coagulants and/or flocculants quickly and effectively, a high-throughput treatability technique (HTTT) was developed. High-throughput platforms involve the use of small scale tests that allow for an efficient study of a variety of process conditions using minimal amounts of material; they have been widely used in the bioprocessing (Kostov et al. 2000, Welch et al. 2002, Bensch et al. 2007) and the chemical production industry (Dar 2004, Merrington et al. 2006). There has been some limited work in the environmental sector – specifically on the use of activated carbon for removal of organic pollutants (Crittenden et al. 1991, Ying et al. 2006, Chang et al. 2007), the development of bio-electrochemical systems (Call & Logan 2011, Ren et al. 2013), and the development of flocculants for the treatment of oil sands tailings (Mohler 2012). Recently a HTTT study was applied to biosolids dewatering (LaRue et al. 2015). In that work, a microplate-based method, requiring less than 5 mL of starting material, was developed to evaluate the performance of different flocculants over a range of dosages.
This paper presents the results and conclusions from two applications of the HTTT method. Case Study A is a treatability screen on tailings reclaim water from a mine in Northern Ontario, Canada. In this case study, ten coagulants and seven flocculants were evaluated at various concentrations and in various combinations to optimize the settling of ultrafine particles. Highlights include 475 distinct treatment conditions performed in less than five days of test work, and an optimized chemical recipe with significant potential OPEX savings. Case Study B is a testing campaign to screen various flocculants, select the best performing flocculant, and optimize the dosage for a lime-precipitated metals sludge at a pigment production plant. This case study involved the screening of over twelve flocculants at various dosages over three pH conditions. The results included over 200 distinct conditions in three days of test work. An optimal flocculant was recommended for pilot testing in the next stage of the project.