Recycled Process Water Research Articles

Impact of Recycled Process Water on Electrochemical Reactivity of Sulphide Ore

The Kevitsa Cu–Ni sequential flotation process is characterised by poor nickel recovery during summer periods (May–September). Evidently, the process water matrix in summer is different from that in other seasons; however, the Cu flotation performance is scarcely affected by the changes in the water matrix across the seasons. Increasingly different process water quality was generated through a grinding-and-dissolution protocol and its impact on the electrochemical reactivity of sulphide ore was studied. The main objective of this approach was to mimic the increasingly different quality of plant process water emanating from a closed-process water loop. Dissolved oxygen demand tests were conducted on the Kevitsa ore using water of varying quality from dissolution loops. The effect of the temperature and fine grind on the oxidation rates was also investigated. The study was coupled with EDTA metal ion extraction and xanthate adsorption tests. These showed that the number of dissolution loops, which has an impact on water quality, has a direct impact on the rate of oxidation of the ore. A fine grind and high temperature both increase the oxidation rates of the ore. The Kevitsa ore is most reactive in the first 10–20 min after milling. Furthermore, oxidation rates are also driven by the amount of pyrrhotite in the ore, with chalcopyrite being the least reactive, as indicated by the EDTA data. Xanthate adsorption is impacted by the water quality and fine grind. The combined effect of water quality, temperature and fine grind is expected to influence the flotation behaviour of sulphide minerals. The poor nickel recovery of the Kevitsa ore during the summer period is attributable to the unfavourable process water quality, which accelerates the oxidation of the ore during the summer period.

Oxidative Dissolution of Low-Grade Ni-Cu Ore and Impact on Flotation of Pentlandite

This paper investigated the effect of mineral surface oxidation on the floatability of Kevitsa low-grade Ni-Cu ore. Physicochemical measurements, ethylene diamine tetra acetic acid (EDTA) extraction, and oxygen uptake experiments were carried out with slurry and recycled process water samples obtained from the Kevitsa Cu-Ni sequential concentrator plant. The pH of recycled process water, copper flotation feed, and nickel flotation feed dropped by 0.7, 0.4, and 0.7 points, respectively, from May to July. The oxygen demand increased from recycled process water to the copper flotation feed, then dropped for the nickel flotation feed. The nickel flotation feed Redox potential (ORP) was lowest for July, while EDTA extractable metals increased from May to July. There was a 20% drop in nickel recoveries from May to July. Based on ORP measurements of the nickel flotation feed, good nickel flotation takes place in a moderately oxidizing (75–170 mV) and alkaline (9.2–9.7 pH) environment. Therefore, the ORP/pH of the nickel flotation feed is important to the nickel flotation. The results showed that at the Kevitsa plant, the grinding process is an electrochemically active environment, which, together with the incoming recycled process water quality, defines the degree of mineral surface oxidation for flotation. The increasing corrosiveness of the recycled process water increased mineral surface oxidation and depressed pentlandite flotation. Laboratory flotation experiments confirmed the observed poor plant flotation response when the corrosiveness of recycled process water increased. Total dissolved solids (TDS) was proven to be a reliable online parameter for the corrosiveness of the recycled process water and was inversely proportional to the pentlandite recovery. The findings of this study may help the plant develop ways to enable a timely response to changes in recycled process water quality to prevent harmful impacts on pentlandite flotation.

The Use of Acid Mine Drainage (AMD) in the Flotation of a Platinum-Group-Minerals-Bearing Merensky Ore

Water scarcity is compelling mining houses to not only recycle process water but to also identify alternative sources of make-up water in concentrators. South Africa has significant volumes of acid mine drainage (AMD) generated from vast mining operations. This study investigated the viability of using AMD as a replacement for potable water in the flotation of a platinum-group-minerals (PGM)-bearing Merensky ore. Rougher and cleaner flotation testwork was conducted at laboratory scale to compare the performances of potable water (baseline water), AMD treated with Ca(OH)2, and AMD treated with the Veolia process. Water analysis showed that the three water types differed in pH, water hardness, conductivity, and total dissolved solids. The results showed the AMD treated with Ca(OH)2 was detrimental to PGM recovery compared to potable water at depressant dosages of 50 g/t. Specifically, AMD treated with Ca(OH)2 achieved a PGM rougher recovery of 67.8%, while potable water achieved a PGM rougher recovery of 88.4%. Depressant dosage optimisation and treatment of the AMD using the Veolia process were investigated as potential strategies to mitigate the detrimental effects of the AMD treated with Ca(OH)2 on the flotation performance of a Merensky ore. The AMD treated with the Veolia process achieved a PGM rougher recovery of 70.8%. Thus, treatment of the AMD was beneficial, though the PGM and base metal sulphides (BMS) recoveries were still lower than those achieved in potable water. Reducing the depressant dosage to 25 g/t in AMD treated with Ca(OH)2 resulted in the highest PGM, Cu, and Ni rougher recoveries of 91%, 60.2%, and 58%, respectively. The AMD treated with Ca(OH)2 at lower depressant dosage outperformed the potable water in terms of PGM and BMS recoveries and concentrate grades, indicating that AMD has the potential to replace potable water as make-up water in Merensky ore processing plants. The results showed that depressant optimisation is important to achieve superior metallurgical results when using AMD treated with Ca(OH)2. The use of AMD in Merensky ore processing plants not only conserves freshwater in minerals processing plants but also reduces high volumes of contaminated effluents.

Deconstruction and valorisation of a mixture of personal protective equipment using hydrothermal processing

This study used non-catalytic hydrothermal deconstruction to examine the deconstruction of a mixture of numerous PPE items, including isolation gowns, gloves, goggles, face shields, surgical masks, and filtering-facepiece respirators. A mixture of PPE items was subjected to hydrothermal deconstruction at temperatures varying between 250 °C and 350 °C and reaction times of 90 min and 180 min, respectively. A reduction of up to 95 % was attained in the total suspended solids (TSS). The total chemical oxygen demand (tCOD) and soluble chemical oxygen demand (sCOD) decreased dramatically to 703 mg/L and 480 mg/L, respectively. Volatile fatty acids, mainly acetic acid and ammonia nitrogen (NH3-N) were the primary end products with a concentration of up to 15,625 mg/L and 38 mg/L after 180 min of deconstruction, respectively. Carbon dioxide and oxygen were found to be the primary gaseous product, with a concentration of up to 14 % (w/w) for CO2 and 76 % (w/w) for O2. Further experiments were conducted at 300 °C and 350 °C to reuse process water for five cycles to demonstrate the feasibility of process water recycling. The results propose that non-catalytic hydrothermal deconstruction may potentially reduce PPE waste by minimising solid waste and water usage.

Techno‐economic evaluation of a process for the transformation of VitAto sweet potato into value‐added products

AbstractVitAto is a popular orange sweet potato (SP) variety in Malaysia that is easy to grow, produces a large yield, and contains more nutritional components. VitAto flour is a significant ingredient in a variety of food compositions; nevertheless, establishing a cost‐effective process design is critical. Five potential process scenarios were built using the SuperPro Designer simulator, with a VitAto plant capacity of 4,000 kg/h and additional income from byproducts such as VitAto juice and VitAto protein. Purchasing cost (PC), capital expenditure (CAPEX), operating expenditure (OPEX), and net present value (NPV) were used to compare the suggested projects in order to find the most efficient and profitable ones. The alternate procedure for producing VitAto juice yields a higher NPV (US$ 13,830,000–US$ 13,867,000/year). According to the data, VitAto juice is the most profitable product, accounting for 52–60% of overall project revenue. As a result, implementing a process with water recycling and byproducts revenue can be a more profitable and long‐term project that will benefit Malaysia's low‐ and middle‐income rural areas.Practical ApplicationsViTAto's current applicability is primarily for traditional meals. It has been recognized that it has a lot of potential in the cookie and baking industries. The VitAto must be turned into flour after harvesting to enable for longer storage. Designing a modernized VitAto flour processing facility with a wastewater treatment facility (process water recycling) is costly and keeping the flour price low is difficult. Therefore, comparing different process design configurations and conducting a techno‐economical study is critical. It is thought that incorporating byproducts into the production process can boost project revenue. As a result, it would benefit farmers in rural areas where VitAto could be marketed at a competitive price. The manufacturing process also produces compostable biomass, which farmers can use in their planted fields. This mutually beneficial relationship between farmers and millers is critical for enhancing their quality of life while also benefiting the environment.

The Evaluation of Starch-Based Flocculant on the Thickener Operation in the Molybdenum Processing Plant and Competency of Molybdenite Flotation

The type and dosage of flocculants used in the middle thickener of the copper-molybdenum plant, in addition to adjusting the quality of recycled process water, is very effective on the floatability of molybdenite. In this study, the effect of starch-based flocculant (wheat starch) was investigated on the efficiency of middle thickener and molybdenite flotation, in the molybdenum processing plant. First, sampling from overflow and underflow of the middle thickener in Mo processing circuit (in industrial scale), in the presence and absence of starch, were collected. The polished sections of samples from the overflow and underflow of the thickener were studied in order to determine the effect of starch on particles settling with different shapes. Microscopic studies show that molybdenite plate-like coarse particles are transferred to the thickener overflow (process water) in the presence of starch flocculant, whereas molybdenite fine particles present in the underflow are often needle-shaped. In addition, in terms of grade distribution, the grade of molybdenum in the thickener overflow is higher than that of copper and iron. Then, after sedimentation tests (in laboratory scale) with different concentrations of flocculant, flotation tests were performed on test samples. According to the results from laboratory studies, increasing the dosage of starch from 0 to 1000 g/t increased the recovery of molybdenite flotation and reduced the access of copper minerals to molybdenite concentrate. In this case, molybdenum recovery (in lab tests) is increased by about 5% compared to the case of not using starch. While the increase in the recovery of molybdenum by adding starch to the middle thickener in the industrial scale is about 10%. In higher dosages of starch (2000 g/t), the trend is reversed (in the lab and industrial scale) and molybdenum recovery decreased sharply due to the decrease in contact angle and depression, whereas the amount of copper transferred to the molybdenum concentrate increased.

Considering Specific Ion Effects on Froth Stability in Sulfidic Cu-Ni-PGM Ore Flotation

The mining and mineral processing of Cu-Ni-PGM sulfide ores in South Africa occurs in semi-arid regions. The scarcity of water resources in these regions has become one of the biggest challenges faced by mineral concentrators. As a result, concentrators are forced to find ways through which they can manage and control their water usage. The recycling and re-use of process water in mineral concentration plants has therefore become a common practice. This practice is beneficial in that it reduces reliance on municipal water and harnesses compliance to stringent environmental regulations on freshwater usage. This approach also offers a better response to the Sustainable Development Goals (SDGs) for the mining industry, as water and its preservation form part of the SDGs. This practice could, however, be somewhat concerning to a process operator because recirculated water often has higher concentrations of ions compared to fresh or potable water. This is because an unintended change in the process water quality may affect critical aspects of flotation such as the stability of the froth. This issue has led to the need for both the mining industry and researchers in the field to find the ions in process water that have the greatest impact on froth stability. Thus, the authors of this study investigated the effects of various ions common in the process water of a typical Cu-Ni-PGM ore on froth stability using a 3 L bench scale flotation cell. Solids and water recoveries were used as proxies for froth stability. These were further complemented by bubble size, water recoveries, foam height, and dynamic foam stability from two-phase flotation systems. A two-phase foam study resulted in observations that supported findings from a three-phase study. Generally, single salt solutions containing Ca2+ and Mg2+ ions resulted in higher water recoveries both in the two-phase foam and three-phase froth studies, increases in foam heights and dynamic foam stability, and a decrease in bubble size compared to the solutions that contained Na+. SO42− also resulted in increased foam stability compared to Cl− and NO3−. These results showed that the divalent inorganic electrolytes—Ca2+, Mg2+, and SO42−—were more froth- and foam-stabilizing than the monovalent inorganic electrolytes—Cl−, NO3−, and Na+. This finding was in agreement with previous research. The findings of this study are deemed crucial in the development of a process water management protocol in sulfidic Cu-Ni-PGM ore concentrators. However, more comparative three-phase froth stability tests are needed as subjects of future investigative work to further ascertain specific ion effects on froth stability in sulfide ores.

Phosphomolybdic acid-catalyzed oxidation of waste starch: a new strategy for handling the OCC pulping wastewater.

When old corrugated cardboard (OCC) is returned to the paper mill for repulping and reuse, the starch, which is added to the paper surface as a reinforcement agent, is dissolved into the pulping wastewater. Most of the OCC pulping wastewater is recycled to save precious water resources; however, during the water recycling process, the accumulation of dissolved starch stimulates microbial reproduction, which causes poor water quality and putrid odor. This problem seriously affects the stability of the papermaking process and product quality. In this study, phosphomolybdic acid (H3PMo12O40, abbreviated as PMo12) was utilized to catalyze the waste starch present in papermaking wastewater to monosaccharides, realizing the resource utilization of waste starch. The results showed that the optimized yield of total reducing sugar (78.68 wt%) and glycolic acid (12.83 wt%) was achieved at 145°C with 30 wt% PMo12 at pH 2, which is equivalent to 91.51 wt% starch recovered from wastewater for resource utilization. In addition, the regeneration of the reduced PMo12 was realized by applying a potential of 1V for 2h. Overall, this study has theoretical significance and potential application value for resource utilization of waste starch in OCC pulping process and cleaner management of OCC waste paper.

Enhancement of a Spent Irrigation Water Recycling Process: A Case Study in a Food Business

Food operations use vast amounts of water. To reduce utility costs as well as concerns regarding water depletion in ecosystems, food businesses usually try to reuse their water. However, this often needs a recycling process to ensure the water is of good quality and safe to reuse in a food environment. This paper presents a case study of a grower of beansprouts and other varieties of sprouted seeds that uses six million litres of water weekly. Approximately 60% of their spent irrigation water is recycled using both 50 µm and 20 µm drum filtration. In addition, chlorine dioxide is used as part of the recycling process as a disinfectant. Our analysis demonstrated that the size of suspended solid particles in over 90% of the cumulative sample tested was smaller than the current 20 µm filter in place, highlighting that the existing system was ineffective. We, then, explored options to enhance the water recycling system of the company. After careful analysis, it was proposed to install a membrane-filtration system with ultraviolet technology to increase the finest level of filtration from the existing 20 µm to 0.45 µm absolute and sterilize any remaining bacteria. This not only improved water quality, but also allowed for the removal of chemicals from the recycling system, delivering both financial and technical improvements.

The Influence of Specific Ions and Oxyhydroxo Species in Plant Water on the Bubble-Particle Attachment of Pyrrhotite.

Previous studies have considered the effect of using recycled process water in froth flotation and whether certain ions are responsible for what is observed in the final concentrate in terms of mineral grades and recoveries. The attachment of mineral particles to air bubbles is a fundamental subprocess of flotation, without which separation of valuable minerals from nonvaluables cannot occur; it is, therefore, of interest to assess the effect of specific ionic species on bubble–particle attachment. The effects of oxyhydroxo species on bubble−particle interactions were studied with three synthetic plant water (SPWs) of increasing ionic strengths at pH 11 as it is known to through solution speciation that at this pH, oxyhydroxo species may be present in significant concentrations. The presence of these oxyhydroxo species such as magnesium and calcium hydroxides in alkaline pulps were confirmed by many researchers and proven to affect bubble and particle surface charges. Furthermore, to ascertain whether there were certain ions within the plant water that impacted the bubble–particle attachment more significantly than others, tests were carried out with carefully selected single salt solutions. The SPWs at pH 11 resulted in very poor pyrrhotite attachment probabilities and recoveries as compared to the attachment probabilities and recoveries that were obtained with these waters at pH 6.5. Increasing the ionic strength of SPWs resulted in a decrease in pyrrhotite attachment probabilities more evidently at pH 11. Thus, it can be concluded that the presence of CaOH+, (MgOH)2, and MgOH+ species hinders the flotation of pyrrhotite particles. Studies on selected single salts showed that Na+ resulted in better pyrrhotite attachment probability and recovery compared to Ca2+. Furthermore, upon studying the anion effect, SO42– performed better than NO3– when paired with Ca2+, thus indicating a negative effect on flotation response when Ca2+ and NO3– ions are used together. These results can be attributed to the action of species such as Ca2+, CaNO3+, and CaSO4(aq.) on the zeta potential and their consequential effect on the electrical double layer. The outcomes of this work should be of significant importance for an effective management of ions in recycled process water in the froth flotation process.

Remediation of reduced sulfur species effects on gold and silver recovery during cyanide leaching

Cyanidation circuits that treat sulfidic ores may contain one or more of the following reduced sulfur species: sulfide (HS−), polysulfides (Sn2−), thiocyanate (SCN−), thiosulfate (S2O32−), trithionate (S3O62−), tetrathionate (S4O62−), pentathionate (S5O62−), hexathionate (S6O62−). The actual speciation of the reduced sulfur species in the circuits will primarily depend on the redox potential, pH, cyanide levels and existing sulfur species in recycled process water, as well as the presence of other reactive metal species. Higher polythionates (i.e. tetra-, penta- and hexathionate) present in leach solutions react with cyanide ions rapidly and consume the available cyanide causing lower metal recoveries at cyanide leaching plants. When higher polythionate ions are degraded to trithionate, cyanide consumption by these ions could be lowered, and metal recoveries would increase.This study presents the sulfur species formed and a practical polythionate degradation method that can be applied within the cyanidation circuits. The possibility of increased gold and silver recoveries and decreased cyanide consumptions by controlling the higher polythionates (SnO62−, n = 3,4,5,6) with the addition of sulfite salts to the cyanide leach slurries was studied. Experimental results showed that average gold and silver recoveries increased by 13.3% and 28.8%, respectively at 500 ppm (mg/L) NaCN and 300 ppm (mg/L) sulfite (SO32−) concentration levels compared to the control experiments where no sulfite was added to the leach slurries. Additionally, higher sulfite concentrations in the leach slurries resulted in lower tetrathionate and higher thiosulfate, trithionate and available cyanide concentrations.

Removal of organic pollutants from rubber wastewater using hydrophilic nanocomposite rGO-ZnO/PES hybrid membranes

The introduction of membrane filtration for rubber wastewater treatment, the utilization of treated wastewater as recycled process water to minimize water demand during processing becomes possible. In this work, novel polyethersulfone (PES) nanohybrid membranes incorporating low loadings of ZnO nanoparticles (NPs), reduced graphene oxide (rGO), and their combination were investigated. Characteristics alteration of the membrane were confirmed using a scanning electron microscope (SEM), Fourier transform infra-red (FTIR), x-ray diffraction (XRD), contact angle, and porosity structure. The SEM images showed a reduction of NPs agglomeration by the addition of rGO. The dual filler rGO/ZnO has exhibited significant improvement in the membrane structure, wettability, and mechanical strength. The modified membranes also exhibited better separation performances as compared to the neat PES membrane. The average permeate flux was enhanced from 2.69 to 11.51 L m−2h. a remarkable pollutant reduction was shown by the chemical oxygen demand (COD), NH3, and turbidity rejection up to 92%, 88%, and 99%, respectively for PES-rGO/ZnO membrane. The flux recovery ratio of the modified membrane was recorded to be 82%, 80.21%, and 83% for PES-ZnO, PES-rGO, and PES-rGO/ZnO, respectively which was 7–12% higher than neat PES membrane. The cleaning under UV light can increase the flux recovery ratio (FRR) up to 14% due to the photocatalytic activity of ZnO and rGO that helped to degrade the organic fouling. The results obtained in this study are expected to have great potential on membrane studies, particularly for high-organic content wastewater treatment.

Probing the Effect of Water Recycling on Flotation through Anion Spiking Using a Low-Grade Cu–Ni–PGM Ore: The Effect of NO3−, SO42− and S2O32−

Water scarcity necessitates the recycling of process water within mineral processing practices. This may however come with its disadvantages for unit operations such as froth flotation as this process is water intensive and sensitive to water chemistry. It is therefore important to monitor the water chemistry of the recycle stream of process water and any other water source to flotation. Monitoring the concentrations of the anions in recycled process water is therefore important to consider as these are speculated to impact flotation performance. Batch flotation tests were conducted using synthetically prepared plant water (3 SPW) with a TDS of 3069 mg/L as the baseline experiment. 3 SPW contained 528 mg/LNO3− and 720 mg/L SO42−, other anions and cations, and no S2O32−. Upon spiking 3 SPW with selected anions, viz, NO3−, SO42− and S2O32−, it was noted that NO3− and SO42− exhibited threshold concentrations while S2O32− did not show a threshold concentration for both copper and nickel grade. Spiking 3 SPW with 352 mg/L more of NO3− to a total 880 mg/L NO3− concentration resulted in the highest copper and nickel grade compared to 3 SPW while increasing the S2O32− from 60 to 78 mg/L increased nickel and copper grade. 720 to 1200 mg/L SO42− and 528 to 880 mg/L NO3− were deemed the concentration boundaries within which lies the threshold concentration above which flotation performance declines with respect to metal grades, while for S2O32− the threshold concentration lies outside the range considered for this study. Anion distribution between the pulp and the froth did not seem to impact the recovery of copper or nickel. Notably, the correlation between the concentrate grades and anion distribution between the froth and the pulp seemed to be ion dependent.

Beneficiation of recycled process water at DRDGOLD's ERGO plant, and its effect on gold recovery

SYNOPSIS To conserve fresh water resources and comply with environmental regulations, DRDGOLD, a South African gold producer re-treating surface tailings, has transitioned to a fully closed water circulation system. Consequently, the accumulation of contaminants, as well as addition of reagents, has led to changes in water composition that have compromised leach performance and overall gold recovery. A two-sample t-test confirmed a significant difference in gold recoveries between the use of Rand Water, which was used as a benchmark, and untreated process water. Atomic absorption analysis of ERGO's process water, confirmed the presence of iron, nickel, zinc, and manganese. A study of the effect of the identified contaminants on gold recovery showed that iron, nickel, and zinc have the largest negative effect on gold recovery, with iron and nickel being more detrimental than zinc. Sulphates were shown to have a possible passivation effect, which also influenced gold recoveries, although to a lesser extent than the heavy metals. Calcium, when present in excess, had a positive influence on gold recovery indicating the possible formation of a calcium aurocyanide complex. Lime softening successfully reduced the heavy metal and sulphate concentrations, and the gold recoveries obtained with the treated process water were similar to those as achieved with Rand Water. Keywords: gold tailings, re-processing, water quality, gold recovery.

Abatement of Inhibitors in Recycled Process Water from Biomass Fermentations Relieves Inhibition of a Saccharomyces cerevisiae Pentose Phosphate Pathway Mutant

Understanding the nature of fermentation inhibition in biomass hydrolysates and recycled fermentation process water is important for conversion of biomass to fuels and chemicals. This study used three mutants disrupted in genes important for tolerance to either oxidative stress, salinity, or osmolarity to ferment biomass hydrolysates in a xylose-fermenting Saccharomyces cerevisiae background. The S. cerevisiaeZWF1 mutant with heightened sensitivity to fermentation inhibitors was unable to ferment corn stover dilute-acid hydrolysate without conditioning of hydrolysate using a fungal strain, Coniochaeta ligniaria, to consume inhibitors. Growth of two other strains, a salt-sensitive HAL4 mutant and a GPD1 mutant sensitive to osmotic stress, was not negatively affected in hydrolysate compared to the parent xylose-metabolizing strain. In recycled fermentation process water, inhibition of the ZWF1 mutant could again be remediated by biological abatement, and no effect on growth was observed for any of the mutants compared to the parent strain.

Industrial application of ceramic nanofiltration membranes for water treatment in oil sands mines

A commercial titania ceramic nanofiltration membrane unit with a permeate flow capacity of 20 m3/h was used to reduce ion concentration, Total Suspended Solids (TSS) and Total Organic Carbon (TOC) in recycle water from a Canadian oil sands mine. This unit, the first of its kind, was tested for almost two years to evaluate membrane performance under actual recycle process water conditions. This paper focuses on the results at a 50% stage cut. A strong correlation between specific flux and rejection was found, with the highest mass rejections observed at the lowest specific flux values. A potential formation of a cake layer on the membrane surface seems to favour the rejection since lower specific flux values improved mass rejection. The analysis of more than 20 ions showed that differences in hydrated ionic sizes and electrostatic phenomena are at play with divalent cations showing the largest rejection. Additional 75–90% TOC and almost 100% TSS rejection was observed. These results indicate that it is possible to implement this technology in an oil sands mine and obtain significant water quality improvements and reducing river water intake.

First insights to the microbial communities in the plant process water of the multi-metal Kevitsa mine

Metallurgical processes demand large quantities of water. However, in many locations, water is becoming scarce and process water recycling is needed. Closing water loops can be challenging due to build-up of flotation chemicals, metal ions and microorganisms in the recycled water affecting the flotation performance. Here, we have characterized the microbial communities over a 2-month period in different locations of the multi-metal Kevitsa mine in Northern Finland, by microbiome sequencing, enumeration of bacteria, archaea and fungi by qPCR, and cultivation. The microbial communities showed high diversity, but were dominated by Alpha- and Gammaproteobacteria. In addition, various fungal taxa were detected, whereas the archaeal taxa were only sparsely detected from the sequence data. The number of bacterial 16S rRNA gene copies in Process water and Ni thickener overflow varied between 0.5–3.3 × 105 mL−1, whereas the Flotation tailings showed two orders of magnitude lower amounts. Fungi were present at 3.0 × 102–8.1 × 104 5.8S rRNA gene copies mL−1 in all samples, while the number of archaea fluctuated between 8.8 × 101–3.2 × 105 16S rRNA gene copies mL−1. The number of all microbial groups were generally lower in September than in August. When tested on 8 different cultivation media, the microorganisms generally responded positively to organic carbon, and were also shown to oxidize thiosulfate, which may indicate that build-up of organic flotation chemicals and sulfur species from the ore may cause the microbial numbers to increase. This study is part of the H2020 ITERAMS project (Grant agreement# 730480), which strives to improve the recycling of water and minimize the environmental impact of mines.

Recycle of fermentation process water through mitigation of inhibitors in dilute-acid corn stover hydrolysate

Water consumption is an important consideration for production of advanced biofuels and chemicals. Recycling process water to reduce water consumption concentrates inhibitors formed during biomass pretreatment processes. To lessen their impact, Coniochaeta ligniaria NRRL 30616 was used to biologically abate inhibitors in dilute-acid pretreated corn stover hydrolysate. Biological abatement of inhibitors enabled recombinant ethanologenic E. coli FBR5 to complete fermentation before cultures using untreated hydrolysate emerged from the lag phase. Biological abatement allowed 50% reuse of the liquor in subsequent fermentations, and hydrolysate could be recycled five times. Although growth of E. coli FBR5 was variable in fermentations using recycled hydrolysate, ethanol productivity was essentially the same as in single-use hydrolysate. In contrast to biological abatement, overliming did not adequately eliminate inhibitors and led to unsatisfactory fermentation results. Bioabatement also enabled recovery of failed fermentations and allowed recycling of spent liquor for use as process water in a corn stover pretreatment process.

Minimizing beneficiation wastewater through internal reuse of process water in flotation circuit

Cost-effective methods for reducing freshwater requirement and wastewater emission in beneficiation processes (particularly in flotation process) are greatly important in the modern mining industry. This study aims to minimize water consumption and wastewater generation in dressing plants by internally reusing process water at certain stages of flotation circuit . Laboratory scale tests demonstrated that locked cycle recycling of process water built up chemical reagents in water, which in turn influenced the flotation performance of valuable minerals and significantly decreased the grade and recovery of concentrates. Changing flotation reagent regimes in response to flotation fluctuations can reliably and feasibly maintain mineral recovery efficiency during the reuse process. Industrial scale tests validated that the quality of concentrates obtained with and without process water reuse did not show any considerable difference and satisfied the product specifications by carefully adjusting the dosage of flotation reagent. The required reagent dosages in the flotation circuit were reduced by more than 10% after using recycled water. Among the required reagent dosages, sodium sulfide (Na 2 S) was sharply reduced by 18.56%. Most importantly, the internal reuse of process water in the flotation circuit minimized freshwater consumption by 34.62% (i.e., from 5.2 t/d to 3.4 t/d), indicating that 525.6 tons of wastewater would no longer be generated every year. Overall, the proposed internal reuse process is a cost-effective and eco-friendly alternative for greening flotation process. • Internal reuse of process water in the flotation process is feasible and reliable. • Changing reagent suite reduces the negative effect of process water on flotation. • Internal reuse of process water minimized water consumed and wastewater emission. • Internal reuse of process water promotes the reutilization of chemical reagents.

Effects of process water recirculation on solid and liquid products from hydrothermal carbonization of Laminaria

Hydrothermal carbonization (HTC) is a promising thermo-chemical technology to treat wet biomasses for production of hydrochars but produces excessive process water. In this study, recirculation of process water from HTC of macroalgae Laminaria was investigated for 12 rounds. Recycling process water increased the hydrochar yield, carbon recovery rate and high heating value from 13.3% to 17.1%, from 22.9% to 32.6%, and from 18.4 MJ/kg to 20.5 MJ/kg after 12 rounds, respectively. The process water recirculation could partly alleviate the toxicity of process water through seed germination test. Volatile fatty acids (VFAs) predominantly accumulate with process water recirculation. The increased proportion of VFAs on chemical oxygen demand could promote methane production of diluted process waters, a 12.3% increase was observed in the round 10, compared with initial process water. These results showed that recycling the process water could reduce water consumption significantly and enhance energy recovery efficiency.