Aluminum Speciation Resulting from Chemical Precipitation of AL-Bearing Acid Rock Discharge

Acid rock discharge (ARD) or acid mine drainage (AMD) formed through the oxidation of sulfide minerals (usually pyrite) is a major source of water contamination impairment in both coal and hard rock mining regions throughout the worldwide. Aluminum, as an environmentally toxic contaminant, is found in some acid rock discharge (ARD) and acid mine drainage (AMD) locations. The composition of ARD/AMD is complex and lead to the effluent Al concentration varied in different conditions. In this study, the possible effluent aluminum concentrations and species of precipitates likely to be formed in Al-bearing ARD/AMD active treatment system was measured and modeled. Accurate models and calibrated are necessary in predicting an expected discharge Al concentration from the Al-bearing ARD/AMD active treatment systems.A series of experiments were conducted to evaluate the effect of sulfate and silica on both suspended and soluble Al concentrations in a laboratory synthesized Al-bearing ARD. The experimental results showed that the presence of sulfate could reduce the soluble Al concentrations due to the formation of Al-sulfate precipitates, basaluminite. The simulation with Mineql+ model shows that solution was in approximate equilibrium with amorphous Al(OH)3 when sulfate was absent. In the cases when sulfate was present, the solution was in equilibrium with amorphous Al(OH)3 solids after 30 minutes of settling, subsequently it became respect to unsaturated with amorphous Al(OH)3, following with the reduction of soluble Al concentration due to the formation of basaluminite. Although most of sludge are in form of amorphous Al(OH)3(s) after short settling time, the molar ratio of Al:S in sludge showed that the fraction of Al-sulfate precipitates increased with settling time and the fraction of Al-sulfate precipitates in ¡°new¡± produced precipitates increased with settling time after 30 minutes. After 48 hours of settling, the molar ratio of Al:SO4 in suspended particles size was close to the theoretical molar ratio of Al:SO4 of basaluminite. Suspended size distribution revealed that the presence of sulfate reduced the particles size in the supernatant, and these small particles remained in the supernatant , following with a relative higher suspended Al concentration. The presence of silica can reduce the soluble Al concentration immediately after pH adjustment due to the formation of Al-silica precipitates. The experimental results also showed that there was interaction between sulfate and silica in experiments. The presence ulfate can enhance the sedimentation of silica in form of Si(OH)4(s) not as Al-silica precipitates. Either sulfate or silica and combination can reduce the suspended particles size. The high level of silica could increase the effluent Al concentration since it can reduce the settleable proportion of particulate Al solids

Study of the characteristics of pollutants in rural domestic sewage and the optimal sewage treatment process: a Chengdu Plain case study

Domestic sewage is an important source of surface water pollution in the rural areas of developing countries, especially in the rural areas of China. In recent years, with the strategy of rural revitalization, China has paid increasing attention to the treatment of rural domestic sewage. Therefore, 16 villages in the Chengdu Plain were selected for the study, and seven indicators were analyzed and evaluated, including pH, five-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD), ammonia nitrogen (NH3-N), total phosphorus (TP), suspended solids (SS) and total nitrogen (TN), in the water samples at the inlet and outlet of the wastewater treatment plant. The concentration of each pollutant in the rural scattered domestic sewage of the Chengdu Plain in Southwest China was obtained, and the concentration of each pollutant in domestic sewage was higher than that in summer. In addition, the preferred process for removing each pollutant was obtained by studying the effects of the treatment process, season and hydraulic retention time on the removal efficiency of each pollutant. The research results provide valuable references for the planning and process selection of rural domestic sewage treatment. HIGHLIGHTS Comparative analysis of the concentration of rural domestic sewage before entering and after leaving the wastewater treatment plant in the Chengdu Plain.; The concept and calculation method of the ‘α’ was proposed.; System removal efficiency (SRE) was used in the selection of optimal sewage treatment plants.; The most suitable removal process for each pollutant is proposed.

Quantitative Evaluation Method for Landscape Color of Water with Suspended Sediment

Landscape water is an important part of natural landscape, and a reasonable assessment of water landscape color is the basis for scientifically evaluating the quality of water landscape. To evaluate water landscape color with different concentrations of sediment objectively and quantitatively, a method of evaluating water landscape color based on hyperspectral technology is proposed to calculate water landscape color. The color spectrum calculation model of the water landscape color was constructed using the Commission Internationale de L’Eclairage spectrum three stimulus system (CIE-XYZ) calculation method and the response relationship among water reflectance, water depth, and sediment concentration. Under the conditions of eliminating as many external factors as possible, using a hyperspectral instrument to measure the reflectance of sediment and water, the response relationship between water depth and sediment concentration and water reflectance is calculated. Water depth and sediment concentration, which did not appear previously, were verified by experiments that proved the reliability of the water landscape color spectrum calculation model. By using different absolute value of chromatic coordinates in the international CIE-XYZ calculation method, a formula for determining the difference in sediment concentration for water landscape color was defined, and the quantitative evaluation method of landscape color of sand-laden water was established. In this research, we found that the predicted water landscape color, quantified by the color spectrum calculation model, is basically consistent with the actual color of landscape water and is basically in line with actual observation about significant difference assessment, which demonstrated the accuracy and reliability of the model. Hence, this research provides a scientific basis for the establishment of other water quality factors to evaluate water color, which makes it possible to quantify the color of the water landscape based on the establishment the color spectrum calculation model

Distribution Characteristics of Phosphorus in the Yarlung Zangbo River Basin

Phosphorus is an important limiting biogenic material. The special topography and climate of the Yarlung Zangbo River Basin generate unique distribution and transport characteristics of total phosphorus (TP). A survey of TP concentration, precipitation, runoff, sediment content, suspended load discharge, and relevant data was carried out for the Yarlung Zangbo River Basin in the last ten years. In combination with the regional geography and social economies, the basic spatial-temporal characteristics of P-water-sediment were analyzed by using the correlation and time series analysis methods. Furthermore, the transport characteristics of P and the main control factors were also studied. The results show that the TP concentration in this basin displays the characteristics of interannual cyclical variation and annual phasic variation, and the peak value appears in the wet season. Among the Yarlung Zangbo River, Nyangqu River, Lhasa River, and Nyang River, the TP concentration is the highest in the Nyangqu River, exceeding 0.4 mg/L several times in the wet season. In this basin, the distribution patterns of the TP concentration are similar to those of the rainfall, runoff, suspended load discharge, and sediment concentration. The coupling property of the TP concentration is the strongest with the suspended load discharge among the meteorological and hydrological parameters. The spatial variation of dissolved P in the wet and dry seasons in 2016 responded to the distribution patterns of the population density, environmental factors, farming, and animal husbandry. This indicates that the TP in the water is mainly from non-point sources and is affected by agricultural, geographical, and ecological factors. The transport of TP is mainly controlled by the suspended load discharge due to precipitation

Synthesis of bifunctional NiFe layered double hydroxides (LDH)/Mo-doped g-C3N4 electrocatalyst for efficient methanol oxidation and seawater splitting

To boost the oxygen evolution reaction (OER) and methanol oxidation reaction (MOR) of pristine NiFe-layered double hydroxides (LDH), the NiFe-LDH/Mo-doped graphitic carbon nitride (NiFe-LDH/MoCN) heterojunction was synthesized herein through hydrothermal method. The establishment of built-in electric field in NiFe-LDH/MoCN heterojunction enhanced the electrochemical oxidation activities towards both seawater splitting and methanol oxidation, via the improving electrocatalyst surface wettability and conductivity. Almost 10-fold enhancement of turnover frequency (TOF) and electrochemical active surface area (ECSA) than pure NiFe-LDH implied more active sites to participate in catalytic reactions via Mo doping and the formation of heterostructure. Moreover, the local charge redistribution demonstrated in the NiFe-LDH/MoCN interface region may favor the adsorption of methanol and OH− in the seawater. The present work may expound the strong coupling interaction and the establishment of built-in electric field in the interface between NiFe-LDH and semiconductor to enhance both methanol oxidation and seawater oxidation for NiFe-LDH

Spatial and Seasonal Distribution and Transportation of Different Forms of Phosphorus in the Middle Reaches of the Yarlung Zangbo River

The Yarlung Zangbo River basin ecosystem is fragile. The distribution and transportation of phosphorus is of great significance for aquatic environmental protection and ecological security. The sequential extraction method and molybdenum antimony anti-spectrophotometry were used to measure the concentrations of different forms of phosphorus in the surface sediments from 15 sampling sites along the middle reaches of the Yarlung Zangbo River and its tributaries. The results show that the total phosphorus concentration in the surface sediments is 194.0~540.7 mg/kg, which is mainly composed of inorganic phosphorus. The concentrations of various phosphorus forms ranked as calcium-bound phosphorus (355.6 ± 86.0 mg/kg) > soluble phosphorus (15.9 ± 10.0 mg/kg) > iron-bound phosphorus (12.4 ± 12.3 mg/kg) > organic phosphorus (9.6 ± 6.1 mg/kg) > occluded phosphorus (9.2 ± 3.8 mg/kg) > aluminum-bound phosphorus (5.4 ± 2.3 mg/kg). On the whole, phosphorus concentration is greater in wet season than dry season. Regarding the spatial distribution characteristics, there are great disparities in the different forms of phosphorus in the middle reaches of the Yarlung Zangbo River. Comprehensive analysis shows that phosphorus of this area is mainly self-generated, and concentration of bioavailable phosphorus is small, demonstrating there will not be a large release. We also drew a “specific triangle„ of the different forms of phosphorus concentrations in the research area and defined the “α„ angle to determine the nutrient status of the overlying water quickly and effectively. Finally, phosphorus flux of the mainstream was estimated. This research may provide information on the phosphorus of Plateau Rivers

The characterization of a novel magnetic biochar derived from sulfate-reducing sludge and its application for aqueous Cr(Ⅵ) removal through synergistic effects of adsorption and chemical reduction

Removal of heavy metals from the aqueous environment via physiochemical adsorption always remains a great challenge owing to the slow kinetics and low removal capacity for the conventional adsorbent. In this study, the sulfate-reducing bacteria (SRB)-rich anaerobic sludge was pyrolyzed for the preparation of magnetic biochar, i.e. SBC-20-500 (SBC: sulfate-reducing sludge-based biochar; 20 denotes the biochar dosage, namely 8 g dried sludge in 400 mL iron solution which is equal to 20 g/L; 500 represents the pyrolysis temperature, i.e. at 500 °C) with tunable pore structure and surface properties towards efficient removal of chromium (Cr (Ⅵ)). The characterization revealed that magnetic biochar SBC-20-500 exhibited higher surface area and larger pore volume compared to non-magnetic SBC-500. Batch experiments on Cr (Ⅵ) removal were performed under different biochar dosages, pH values, initial Cr (Ⅵ) concentrations and temperatures. The results illustrated that magnetic biochar demonstrated much larger Cr (Ⅵ) adsorption capacity with qe of 5.3585 mg/g as compared to non-modified one (qe = 0.7206 mg/g). The maximum Cr (Ⅵ) removal efficiency of SBC-20-500 reached approximately 93.7% within 24 h under the conditions of pH = 3.0, biochar dosage = 0.8 g and initial Cr (Ⅵ) concentration = 50 mg/L. The kinetic and isotherm fitting results suggested that the pseudo-second-order kinetic and Langmuir isotherm model were more suitable for describing the adsorption behavior of Cr (Ⅵ) by SBC-20-500. The XPS and FTIR results confirmed that chemical reduction of Cr (Ⅵ) to Cr (Ⅲ) also played a role in Cr (Ⅵ) removal in the presence of SBC-20-500. Moreover, the Cr (Ⅵ) removal capacity could still achieve 3.50 mg/g even after five adsorption-desorption cycles, indicating the satisfactory reusability of the as-prepared biochar. The results of this study may provide a win-win approach for simultaneous resource recovery from the wasted sulfate-reducing sludge (SRS) and highly-efficient remediation of Cr (Ⅵ)-contaminated environment.This work was financially supported by the Fundamental Research Funds for Central Universities (No. 3102019AX18 and No. 310201911cx021) and the National Training Programs of Innovation and Entrepreneurship of China (No. S20210699353)