Coal Leachate Research Articles

Production of vanadyl sulfate electrolyte from stone coal acidic leaching solution using mediation solvent extraction-complex reductive stripping method

In this study, a new method for vanadium extraction and separation from acidic stone coal leaching solution was proposed. With the addition of H2O2 in the solution, the positive vanadium VO2+ ion in the solution was converted into anionic di-peroxo vanadium VO(O2)2- ion. Using methyl tri-octyl ammonium chloride (N263) + n-octanol + sulfonated kerosene as extractant, vanadium was fully separated from Fe (III) and other metal impurities during the extraction process. Under the conditions of 10 % N263, 10 % n-octanol, reaction time 10 min, and O/A ratio 1:1, 99 % of vanadium was extracted into the organic phase. After extraction, an organic phase containing V and Mo was obtained. Due to low solubility of V (V) in acidic solution, oxalic acid was mixed with sulfuric acid solution and employed as complex-stripping solution. It was found that oxalate ion formed a complex with V (V), which could break the solubility barrier of V (V) in acidic solution, realizing the direct stripping of V (V). The effect of oxalic acid amount and temperature on the stripping process were investigated, the results showed that increase in oxalic acid amount and reaction temperature favored vanadium stripping. Under conditions of 25 % H2SO4, oxalic acid concentration of 1 g/L, 80 °C temperature, reaction time 50 min, and O/A ratio of 6:1, 99.7 % of vanadium was stripped into the aqueous solution. The vanadyl sulfate product obtained was compared with standard vanadium electrolyte, and it was found that vanadyl sulfate obtained by this method meets the requirements of vanadium electrolyte relevant standards. This paper proposed a new process for high purity vanadyl sulfate production from acidic stone coal leaching solution, which could provide a reference for Vanadium Redox Flow Batteries (VRFB) industry.

Preparation of lightweight ceramsite by stone coal leaching slag, feldspar, and pore-forming reagents

In this study, lightweight ceramsite was prepared by stone coal leaching slag (SCLS), feldspar, and various pore-forming reagents via the roasting process, and the effect of raw meal ratio, roasting temperature, and roasting dwelling time on ceramsite features was investigated through orthogonal and single-factor experiments. The bulk density of ceramsite decreased from 900.0 to 762.0 kg/m3 when the content of Fe2O3 increased from 0 to 6 %. Under the optimal conditions (SCLS: feldspar: Fe2O3 = 65: 29: 6 and roasting at 1150 °C for 25 min), the ceramsite possessed a bulk density of 762 kg/m3 and water absorption of 2.4 %, which meet the Chinese standards for ceramsite (GB/T 17431.1–2010). The adsorption of the ceramsite was then characterized by different adsorption models and adsorption–desorption curves. The specific surface area of prepared ceramsite was 1.717 m2/g, which was suitable to produce adsorption materials. X-ray diffraction (XRD) results showed that the peak intensity of quartz and feldspar decreased and the cristobalite phase appeared with the increase in temperature, which helps to enhance the strength of sintered ceramsite. The major crystalline phases of the prepared ceramsite were quartz, feldspar, hematite, and cristobalite at 1,150 °C. The leaching concentration of heavy metals in ceramsite was far below the limited value of GB 5085.3–2007, which means that heavy metals were wrapped inside ceramsite. This study demonstrates a practical use for SCLS, potentially eliminating its damage to the environment, and provides guidance for SCLS-based ceramsite production.

Synthesis of eco-friendly ZnO-based heterophotocatalysts with enhanced properties under visible light in the degradation of organic pollutants

Heterogeneous photocatalysts have been widely used for the removal of various organic pollutants from wastewater. The main challenge so far resides in the sustainability of the process, with regard to the synthesis and the application under visible light. In this study the precipitated materials from the Moringa oleifera seed (MO), groundnut shells (GS) and apatite (A) agrowastes were functionalized with zinc oxide (ZnO) and silver (Ag) solution, to produce a novel bioheterophotocatalysts. Various analytical techniques such as scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), photoluminescence (PL) and X-ray diffraction (XRD) were used for the characterization of the novel photocatalysts. It was proven that agrowastes can also enhance the photocatalytic activity of a ZnO-based photocatalyst as pure metals. The combination of MO/GS/A/ZnO/Ag in a 1:1:1 ratio resulted in a lower band gap of 1.59 eV, as compared to the band gap of 2.96 eV for ZnO/Ag. These photocatalysts' efficiency was also tested on the photodegradation of polycyclic aromatic hydrocarbon (PAHs) derived from coal leaching in various water sources such as acidic mine drainage, alkaline mine drainage and sewage wastewater. From MO/GS/A/ZnO/Ag, the removal efficiency was found to be 69.59%, 61.07% and 61.68%, compared to 52.62%, 37.96 and 44.30% using ZnO/Ag in acidic mine drainage, alkaline mine drainage and sewage wastewater for 60 min under solar irradiation.

COAL ION EXCHANGE TO REDUCE NA LEVELS BY UTILIZING ACID MINE WATER

Coal leaching by using mine acid water and solution Mg2+ can reduce the levels of ash and alkali to their needed grade. This demonstrates the ongoing leaching process of ion exchange between the ions contained in coal and with ions contained in the solution. Coal can act as an ion exchanger due to its hollow structure that could contain alkali and earth-alkali ions in its cavities. Thus the alkali ions can be exchanged with other ions in solution. Coal has more adsorption affinity to divalent alkali ions such as Mg2+ and Mn2+ compare to monovalent alkali ions such as Na+. For an ion with the same charge the ion with a smaller volume would be preferred due to the relaxation of matrix contraction within the exchange. The first phase of leaching was conducted to understand the Na content level trend on coal by comparison to Na solution content. The procedure of the study is as follows: first coal is leached with mine acid water, second, the pulp is drained and count the Na, Mg, and Mn content, and third make the graph using the calculation.

Preparation of Lightweight Ceramsite by Stone Coal Leaching Slag, Feldspar, and Pore-Forming Reagents

Preparation of Lightweight Ceramsite by Stone Coal Leaching Slag, Feldspar, and Pore-Forming Reagents

Coal cleaning through removal of phosphorus mineral from morupule main seam coal

ABSTRACT Phosphorus is critical for the strength of metals; however, in excess it makes the metal product fragile. This leads to quality complaints and financial losses. Phosphorus is finely disseminated in coal and forms part of the coal structure. Despite the use of a coal facility at Morupule, the final product surpasses the maximum limit of 0.02% phosphorus. Reduction of the phosphorus by convectional coal cleaning processes is a challenge due to the mineral associations with the coal structure. Selective mining is the current implemented option at Morupule to attain the low phosphorus production but it is costly and time-consuming. Hence, the aim of the research to investigate coal leaching as a primary method for phosphorus reduction. Hydrochloric acid at 1 Mol concentration was used for 4 hours at room temperature. Sixty-four percent phosphorus removal was achieved resulting in 0.012% residual phosphorus. To improve the rate of reaction, microwave pretreatment was conducted to further reduce the amount of phosphorus in the coal. The effect of phosphorus reduction using 1000 W single-mode cavity was compared to that of the multimode cavity. The optimum processing parameters were 2 minutes and 3 hours leaching time to yield a residual phosphorus of 0.008%.

Raman Characteristics of Kuznetsk Basin Coal and Coal-Based Sorbents

Coal samples and the sorbents derived from them are investigated by Raman spectroscopy. A correlation is established between the formation of a developed sorbent surface by the leaching of coal and the degree of graphitization calculated from the Raman spectra. An inverse correlation is found between the metamorphic development of the initial coal and the specific surface of the derived sorbent.

Study on regeneration of spent hydrochloric acid in chemical coal leaching process

For Indian coals, chemical leaching process has better advantage over the conventional physical cleaning techniques due to its drift origin. Coal leaching is a two-stage process where alkali and acid leaching cycles are used, where most of the ash constituents are accumulated in the spent acid and hence purification of spent acid containing silica, alumina, iron, calcium and magnesium is of great importance. Four different methods namely adsorption using activated carbon, ion exchange with anion exchange resin, pyrohydrolysis and stage-wise neutralisation are studied. Results with adsorption and ion exchange techniques are poor and a maximum of 50% removal is observed. Results indicate that, pyrohydrolysis shows better performance with > 99% pure hydrochloric acid as product but it is energy intensive. Stage-wise neutralisation technique is promising for dilute acid, where silica is precipitated by digestion and it produces magnesium oxide and calcium salt with 86.7% and 93.86% purity respectively.

Study on regeneration of spent hydrochloric acid in chemical coal leaching process

Study on regeneration of spent hydrochloric acid in chemical coal leaching process

A review of processing technologies for vanadium extraction from stone coal

ABSTRACT Due to the poor vanadium recovery of mineral processing, the extraction of vanadium from stone coal is directly carried out by metallurgical processes. Salt process, acid process and alkali process three types of stone coal leaching including nine technologies are introduced. However, all of these nine leaching technologies have serious disadvantages and up to now the stone coal has not been efficiently utilised. Chemical precipitation, ion exchange and solvent extraction all can be used to extract vanadium from stone coal leach solutions. Due to the low extraction of vanadium, Chemical precipitation method is rarely used. Ion exchange is only used for the extracting of V(V) from the leach solution. For the extraction of low valence, P204 is one of effective extraction agent. The lately developed technology, LTSRWL, is characterised by high recovery of vanadium, comprehensive recovery of other valuable elements and environmental friendliness, which make it become the best option.

XRF analysis of coal bioleaching by chemolithoheterotrophic Alicyclobacillus HRM5 and chemolithoautotrophic Acidithiobacillus ferrooxidans

Most studies on sulfur bioleaching from coal depend on an autotrophic microorganism with a low growth and a long leaching time. For this reason, heterotrophic heat and acidic pH-resistant Alicyclobacillus was used as the growing and resting cells for the sulfur and iron removal from coal. The results obtained were analyzed by XRF. The data showed that 26.71% of sulfur was removed by Alicyclobacillus in a few days; however, 49.07% of sulfur was removed by Acidithiobacillus in 30 days. This was interesting since the leachings of zinc, strontium, titanium, and iron by Alicyclobacillus, obtained in a few days, were almost the same as the leachings by Acidithiobacillus in 30 days. The results obtained also showed that the Alicyclobacillus cells growing at 55 ˚C removed most of the coal impurities without any change in the carbon content of this fuel. To the best of our knowledge, coal leaching by Alicyclobacillus is reported for the first time.

Optimization of vanadium (IV) extraction from stone coal leaching solution by emulsion liquid membrane using response surface methodology

In order to further improve the vanadium (IV) extraction from stone coal leaching solution in one step and reduce the reagent consumption by emulsion liquid membrane (ELM), the experiments using response surface methodology (RSM) was investigated. The liquid membrane was composed of paraffin as membrane stabilizer, D2EHPA as mobile carrier, span80 as surfactant and H2SO4 as stripping solution. Emulsification speed and emulsification time in emulsion formation was optimized to obtain a stable emulsion. An orthogonal 24 Box–Behnken design (BBD) having five replicates at the center point was used to estimate the coefficients of the response function. The linear effects, square effects and interactive effects of the parameters were analyzed by ANOVA. In addition, the signification of the parameters was also ranked. In the further study, the effect of electric demulsification and membrane recycle ability were studied under the optimized parameters. All of the results revealed that RSM was successfully used to optimize the extraction of V (IV) via ELM and indicated the potential industrially application for vanadium concentration and purification in one step from stone coal acid leaching solution.

In situ reclamation of closed coal mine waste in Korea using coal ash

Adding coal ash to acid waste decreases its acidity and supplies essential nutrients to plants. The effects of coal ash on acid coal mine waste and acid mine drainage were investigated in the field. Treatments were mixtures of coal mine waste with coal ash (0, 20, and 40%). Addition of coal ash increased the pH of coal mine waste and leachate by 3.11 and 3.03 units, respectively. After stabilization, the concentrations in the leachate decreased from 4.65 to 0.44 mg L−1 for Fe and from 0.31 mg L−1 to “not detected” for Pb. The organic matter content and cation exchange capacity increased significantly (approximately twofold each), for coal mine waste with coal ash. Moreover, plant growth on coal mine waste that had been treated with coal ash was greatly stimulated. The application of coal ash offers an environmentally compatible, cost-effective way to remediate coal mine waste or leachate contaminated with heavy metals.

Hydro-geochemical characterization of Milan-Po Plain Area

Despite the aquifers in the Milan metropolitan area are a valuable groundwater resource for a large population (1,336,364 inhabitants in the Milan Municipality; 3,195,629 in the metropolitan area, data at November 2014) and a highly industrialized area, a hydro-geochemical characterization is still missing. In this study, we perform a hydrochemical analysis of the groundwater in the Milan metropolitan area through concentration maps, probability plots and concentration versus depth plots for some major ions (Ca2+, Na+, Cl-, SiO2), trace elements (As, Fe, Mn) and for two common contaminants (NO3- and SO42-) usually deriving from a mixture of point, multipoint and diffuse sources such as leaky sewers, coal gasification work, landfill leachate, septic effluent, house building and recreational areas. In order to attain this characterization, we built a complete and reliable geodatabase concerning the physical and chemical characteristics of the groundwater, starting from multiple different datasets. This database (covering the period 1983-2014) has been explored by classical and multivariate statistical analyses to provide relationships among the more influential lithological, hydrogeological and hydrochemical variables associated to the presence of specific elements and contaminants. The interaction between the phreatic aquifer and the semi-confined/confined aquifer has been also analysed.

Effects of coal contamination on early life history processes of a reef-building coral, Acropora tenuis

Successful reproduction and larval dispersal are important for the persistence of marine invertebrate populations, and these early life history processes can be sensitive to marine pollution. Coal is emerging as a contaminant of interest due to the proximity of ports and shipping lanes to coral reefs. To assess the potential hazard of this contaminant, gametes, newly developed embryos, larvae and juveniles of the coral Acropora tenuis were exposed to a range of coal leachate, suspended coal, and coal smothering treatments. Fertilisation was the most sensitive reproductive process tested. Embryo survivorship decreased with increasing suspended coal concentrations and exposure duration, effects on larval settlement varied between treatments, while effects on juvenile survivorship were minimal. Leachate exposures had negligible effects on fertilisation and larval settlement. These results indicate that coral recruitment could be affected by spills that produce plumes of suspended coal particles which interact with gametes and embryos soon after spawning.

Investigation of Humate Extraction from Lignites

ABSTRACTThe present study investigated the extraction of humate from low-quality lignite samples acquired from Malkara and Yatagan coal deposits in Turkey. The experiments were conducted on finely ground representative coal samples at atmospheric pressure and room temperature. The samples were first leached with concentrated nitric acid for up to 72 hours and undissolved solids were removed by filtration. Potassium hydroxide was added to the leachate for alkalization in order to produce nitro-humic acid solution at different pH levels. Humic matter precipitation was achieved by addition of diluted nitric acid. The extraction products were investigated by proximate, Fourier Transform Infrared Spectroscopy (FTIR), and elemental analyses. The most important factors affecting humate extraction were found to be the consumption of nitric acid dosage for coal leaching, pH value of the leachate after potassium hydroxide addition, and mixing time. The promising results with over 80% humate extraction were achieved for the Yatagan lignites when the acid–coal consumption ratio was less than 1 mL concentrated nitric acid per 1 gram coal at a pH of 9 with mixing for 48 hours, while Malkara lignites reached 70% humate extraction with 72 hours of mixing under the same conditions.

Heterotrophic Bioleaching of Sulfur, Iron, and Silicon Impurities from Coal by Fusarium oxysporum FE and Exophiala spinifera FM with Growing and Resting Cells

Coal is the most abundant fossil fuel containing sulfur and other elements which promote environmental pollution after burning. Also the silicon impurities make the transportation of coal expensive. In this research, two isolated fungi from oil contaminated soil with accessory number KF554100 (Fusarium oxysporum FE) and KC925672 (Exophiala spinifera FM) were used for heterotrophic biological leaching of coal. The leaching were detected by FTIR, CHNS, XRF analyzer and compared with iron and sulfate released in the supernatant. The results showed that E. spinifera FM produced more acidic metabolites in growing cells, promoting the iron and sulfate ions removal while resting cells of F. oxysporum FE enhanced the removal of aromatic sulfur. XRF analysis showed that the resting cells of E. spinifera FM proceeded maximum leaching for iron and silicon (48.8, 43.2%, respectively). CHNS analysis demonstrated that 34.21% of sulfur leaching was due to the activities of resting cells of F. oxysporum FE. Also F. oxysporum FE removed organic sulfur more than E. spinifera FM in both growing and resting cells. FTIR data showed that both fungi had the ability to remove pyrite and quartz from coal. These data indicated that inoculations of these fungi to the coal are cheap and impurity removals were faster than autotrophic bacteria. Also due to the removal of dibenzothiophene, pyrite, and quartz, we speculated that they are excellent candidates for bioleaching of coal, oil, and gas.

Leaching of Trace Elements from Indian Coal

Abstract Metal contamination due to coal leaching has caused various detrimental health hazards in the vicinity of mining industries. To evaluate the release of metal upon weathering under natural condition, aqueous leaching experiments of three different coal samples, from three coalfields - Neyveli, West Bokaro and Makum, were carried out. These coalfields represent three contrasting geological settings. Concentration of Cu and Cr in West Bokaro, and Ni in Makum coal exceeds that of world range. Leachate from Makum coal is highly acidic and contains very high concentration of Fe, Ni, Pb, Mn and Cd. This is mainly caused due to the dominance of pyrite in coal. On the other hand, coals from other mines release near neutral to slightly alkaline leachate. Leachate quality is mainly controlled by the mineralogy, which is a manifestation of depositional environment. Therefore, proper care needs to be taken during storage and dumping of coal at Makum area in order to control the metal contamination.

Maximizing Demineralization during Chemical Leaching of Coal through Optimal Reagent Addition Policy

Abstract The main objective of the optimal reagent addition was to maximize the quantity of product with minimal quantity of feed. In the present study, the optimal addition of reagents during the chemical leaching of coal was computed. Chemical leaching of coal was carried out using aqueous solution of caustic to dissolve and remove the mineral matter. Simulation studies were carried out using the optimal reagent addition for chemical leaching of coal in batch reactors. This was experimentally validated, using the bench-scale reactor setup with hierarchical optimization architecture. Chemical leaching experiments were conducted using West Bokaro coal. Samples collected at various time intervals during the experiment were analyzed. Variations in silica (SiO2) and alumina (Al2O3) concentrations, which were main constituents present in coal ash, were evaluated with respect to time for different concentrations of caustic. The simulation studies for optimal addition were carried out at 6, 8 and 10 intervals. An objective function, required for maximum ash removal, was solved, using sequential quadratic programming (SQP) algorithm to find out the optimum sequence for reagent dosing. An improvement of about 1% (wt) ash reduction on an average was observed with implementation of optimal reagent addition.

Instrumentation and automation system at coal leaching pilot plant

Automation added with intelligent relays and instruments makes implementation of coal leaching pilot plant safe, maintenance free and less dependence upon man power. Two levels of automation have been implemented. Started with data acquisition through controllers overall supervision with supervisory control and data acquisition (SCADA) followed by supervision and data logging by supervisory server have been effectively achieved. Ladder logic programming is done in control logix PLC from M/s Rockwell after building logic sequence, control loops and interlocks of coal leaching process. HART-based instruments are mostly used as field instruments due to smart sensors technology.