Sulfate Precipitation Research Articles

Degradation processes of iron-sulfides and calcite containing aggregates from asphaltic mixtures

Iron-sulfide and calcite containing aggregates used for preparation of asphalt mixtures underwent degradation processes under atmospheric conditions. Four locations with specific secondary mineral phases situated on highways and roads from Transylvania (Romania) were investigated. The mineralogical investigations performed on aggregates as well as on the resulted secondary phases revealed the presence of two types of degradation processes: sulfate precipitation, and carbonation. Iron sulfides such as pyrite and marcasite of hydrothermal origin identified in aggregate grains are the source for iron and acidity. During the wet and warm season, in the presence of atmospheric water and oxygen, in a relatively short time (up to two months) iron-sulfides are transformed and sulfate minerals such as melanterite, rozenite, szomolmokite, copiapite, halotrichite and gypsum precipitate. They are associated with secondary calcite, clay minerals and sulfur. Secondary calcite is the result of carbonation process which is mainly controlled by the acid environment generated by atmospheric CO2 dissolved in the rain water. Another source of acidity is the presence of sulfuric acid resulted during the iron-sulfides degradation process. All secondary products are accompanied by Fe-oxihydroxides of rusty color. Thereafter, the resulted sulfate minerals, which later are easily leached by rainwater, progressively consume the iron-sulfides from the aggregate. This process leads to mechanical disintegration of the grains, progressive stripping and potholes. Secondary calcite is found filling the pores of the asphalt mixture or coating the aggregate grains. Later, it could be dissolved by rainwater.

Crusted scabies in patients with long-term use of oral corticosteroid with different underlying diseases – case series

People with a weakened immune system may develop the severe form of scabies called crusted scabies. We have two cases of female patients with history of using long-term oral corticosteroid and then developing scabies infection. The first patient had other comorbidities which caused her become more susceptible while the second patient had been diagnosed with bullous pemphigoid. Both patients complained thick crust on some parts of their bodies, accompanied with itchy papules. Based on microscopic examination from lesion scraping, we found the adult form of sarcoptes scabiei and crusted scabies diagnosis was established. The lesions were improving when they got combination of topical sulfur precipitate, salicylic acid, and permethrine 5%. Crusted scabies is characterized by hyperkeratosis and crusting of the skin due to the profuse proliferation of mites resulting from an altered host response. Combination of topical antiscabies and keratolytic can make the crusts thinner and improve topical absorption.

Direct analysis of 210Pb in drinking water by liquid scintillation counting after sulfate precipitation

Lead-210 in drinking water can be rapidly determined by liquid scintillation counting (LSC) using a new sulfate precipitation method. In this method, 210Pb was first preconcentrated from water using iron hydroxide co-precipitation followed by sulfate precipitation to decontaminate most of non-alkaline earth elements. The Pb in the sulfate precipitate was then dissolved in strong alkaline solution, while alkaline earth elements (Sr, Ba, Ra) were separated as the sulfate/carbonate precipitate. To optimize the method, the influences of different acids and sulfate concentration on sulfate precipitation as well as the effects of pH, the added SO42−/CO32− concentrations and the Sr/Ba contents in the sulfate precipitate on the dissolution of PbSO4 were studied. In addition, X-ray fluorescence (XRF) analysis was applied for rapid determination of the chemical recovery and triple-to-double coincidence ratio (TDCR) quench correction curve for counting of 210Pb by LSC was established. The method was validated using 5 L of tap water samples and minimum detectable activity concentration (MDC) of ∼0.016 Bq·L−1 was achieved, which is sufficiently sensitive to meet the guidance level of 0.1 Bq·L−1 for 210Pb in drinking water as recommended by the World Health Organization (WHO).

High ACC deaminase producing copper and nickel tolerant rhizobacteria enhances metal tolerance and seedling growth of Indian mustard plant

This study incorporated stable isotope analyses with chemical analyses to determine the origin and migration of sulfur sources in East Asia, and these findings were compared with our decadal research from 2000 to 2001 and 2002 to 2003. The multiple sulfur isotope composition (32S, 33S and 34S) of the dissolved sulfate in precipitation was first measured from 2011 to 2013 in Seoul, South Korea. The δ34Snss values were −1.1‰ to 7.9‰ (avg. 3.6‰), strongly suggesting that sulfur derived from the combustion of Chinese coal is the predominant source of sulfate in the Seoul region. Low NO3/SO42− ratios in the precipitation samples indicated an insignificant effect of sulfur from vehicle exhaust. The seasonal variation of δ34Snss values appears to be caused by increasing biogenic sulfur activity during the spring and summer seasons. The some Δ33S values (0.13‰–0.16‰) measured in the three samples were sufficiently small; thus, whether these values can be attributed to mass-independent fractionation remains unclear. Measuring the Δ33S anomalies in dissolved sulfate provides valuable insights for identifying the sources of sulfur transferred from the stratosphere to the troposphere and upper troposphere.

Sulfate removal from acid mine water from the deepest active European mine by precipitation and various electrocoagulation configurations

Sulfate removal from mine or process water is a key issue in the mining industry. In this paper, precipitation with lime (calcium oxide) was integrated with electrocoagulation for sulfate removal from Pyhäsalmi/Finland mine water. Sulfate precipitation with calcium oxide decreased the sulfate concentration from 13,000 mg/L to 1600 mg/L. Various current densities were applied to the pre-treated mine water with various electrodes and aluminium and iron anodes. It was found that 25 mA/cm2 was the best tested current density for both anode types. At the second stage, this current density was used for different iron and aluminium anodes in various monopolar and bipolar configurations. It was found that this hybridisation is effective for sulfate removal, and that a bipolar configuration showed better results than the monopolar configuration. The best result was gained from 25 mA/cm2 with a two aluminium and two stainless steel anode–cathode configuration and calcium oxide pre-treatment to reach pH 12. The removal efficiency reached 84.4% and 63.8% with aluminium anodes in bipolar and monopolar configurations, respectively. This setup was able to decrease sulfate concentrations from 13,000 mg/L to 250 mg/L, which meets mine water discharge limits. Kinetic studies showed that iron and aluminium anodes obey pseudo-second order kinetic. Finally, the energy consumption was calculated.

Variations in Dissolved Nitrate, Chloride, and Sulfate in Precipitation, Reservoir, and Tap Waters, Columbus, Ohio.

Urban potable waters can be very susceptible to human activities that can impact water quality and, hence, public health. Columbus, Ohio, is currently the 14th largest city in the United States with an estimated population of ~860,000. Much of the urban population receives its water supply from a series of reservoirs located north of the city proper. These reservoirs are fed by river systems that drain either large agricultural lands, or rapidly growing suburban areas, or both. The agricultural activities introduce dissolved nitrate, and increased usage of de-icing salts on roads and highways within the drainage area introduce chloride into the river/reservoir systems. High nitrate in drinking water poses a potential health risk, particularly to infants, while high chloride, applied as halite, in drinking water can aid in the development of cardiovascular disease. In this work, we present a 19-month time series measuring nitrate, chloride, and sulfate in local precipitation, reservoir and household tap waters in order to better understand the relationship of the hydrologic residence time on the tap water chemistry, as well as to evaluate the anion concentrations. The highest chloride tap water concentration, 6.9 mM, occurred in early February 2011, while increases in nitrate occurred in both early summer and the middle of winter. In general, the anion concentrations in the precipitation are all equal to or lower than the reservoir waters. Similarly, the tap water had concentrations of chloride and sulfate higher than reservoir water, while nitrate was similar to reservoir water. Tap water had higher fluoride and sulfate concentrations, suggesting that they are added during the treatment of the reservoir water prior to residential distribution. These data clearly demonstrate the importance of watershed lands on the quality of water in the human distribution system.

A comprehensive model for dynamic characteristic curves considering sulfur deposition in sour carbonate fractured gas reservoirs

Calculating sulfur deposition is a key issue in developing sour gas reservoirs, where sulfur solubility plays an important role. However, prediction of sulfur solubility is a difficult problem due to the toxic of H2S. In this work, an analytical model for dual porosity media considering the influence of sulfur deposition was proposed. The Douglas-Jones predictor-corrector method is used to calculate a relationship between time and pressure, which can avoid solving the system of nonlinear equations. The effects of sulfur deposition on well performance were analyzed and some dynamic characteristic curves for predicting sulfur deposition were provided. The results show that the fastest pressure drop appears near the wellbore, which is the primary damage zone for elemental sulfur precipitation and deposition. Flow parameters and storage ratio play the significant influences on the sulfur saturation curve shape. In addition, the reduction of flow parameters and storage ratio lead to the increase of sulfur saturation and decrease of permeability, resulting in the damage of sour gas formation. The advantage of this approach is that it can be used to describe a characteristic curve without considering the sulfur solubility issue. This paper provides a novel method to analyze the impacts of sulfur deposition on well performances in sour carbonate fractured gas reservoirs.

Alkali enhanced biomass gasification with in situ S capture and novel syngas cleaning. Part 1: Gasifier performance

Previous research shows that alkali addition in entrained flow biomass gasification can increase char conversion and decrease tar and soot formation through catalysis. This paper investigates two other potential benefits of alkali addition: increased slag flowability and in situ sulfur capture.Thermodynamic equilibrium calculations show that addition of 2–8% alkali catalyst to biomass completely changes the chemical domain of the gasifier slag phase to an alkali carbonate melt with low viscosity. This can increase feedstock flexibility and improve the operability of an entrained flow biomass gasification process. The alkali carbonate melt also leads to up to 90% sulfur capture through the formation of alkali sulfides. The resulting reduced syngas sulfur content can potentially simplify gas cleaning required for catalytic biofuel production.Alkali catalyst recovery and recycling is a precondition for the economic feasibility of the proposed process and is effected through a wet quench. It is shown that the addition of Zn for sulfur precipitation in the alkali recovery loop enables the separation of S, Ca and Mg from the recycle. For high Si and Cl biomass feedstocks, an alternative separation technology for these elements may be required to avoid build-up.

Volcano-hydrothermal system and activity of Sirung volcano (Pantar Island, Indonesia)

Sirung is a frequently active volcano located in the remote parts of Western Timor (Indonesia). Sirung has a crater with several hydrothermal features including a crater lake. We present a timeseries of satellite images of the lake and chemical and isotope data from the hyperacid hydrothermal system. The fluids sampled in the crater present the typical features of hyperacidic systems with high TDS, low pH and δ34SHSO4–δ34SS0 among the highest for such lakes. The cations concentrations are predominantly controlled by the precipitation of alunite, jarosite, silica phases, native sulfur and pyrite which dominate the shallow portions of the hydrothermal system. These minerals may control shallow sealing processes thought to trigger phreatic eruptions elsewhere. Sparse Mg/Cl and SO4/Cl ratios and lake parameters derived from satellite images suggest gradual increase in heat and gas flux, most likely SO2-rich, prior to the 2012 phreatic eruption. An acidic river was sampled 8 km far from the crater and is genetically linked with the fluids rising toward the active crater. This river would therefore be a relevant target for future remote monitoring purposes. Finally, several wells and springs largely exceeded the World Health Organization toxicity limits in total arsenic and fluoride.

The origin and migration of the dissolved sulfate from precipitation in Seoul, Korea

This study incorporated stable isotope analyses with chemical analyses to determine the origin and migration of sulfur sources in East Asia, and these findings were compared with our decadal research from 2000 to 2001 and 2002 to 2003. The multiple sulfur isotope composition (32S, 33S and 34S) of the dissolved sulfate in precipitation was first measured from 2011 to 2013 in Seoul, South Korea. The δ34Snss values were −1.1‰ to 7.9‰ (avg. 3.6‰), strongly suggesting that sulfur derived from the combustion of Chinese coal is the predominant source of sulfate in the Seoul region. Low NO3/SO42− ratios in the precipitation samples indicated an insignificant effect of sulfur from vehicle exhaust. The seasonal variation of δ34Snss values appears to be caused by increasing biogenic sulfur activity during the spring and summer seasons. The some Δ33S values (0.13‰–0.16‰) measured in the three samples were sufficiently small; thus, whether these values can be attributed to mass-independent fractionation remains unclear. Measuring the Δ33S anomalies in dissolved sulfate provides valuable insights for identifying the sources of sulfur transferred from the stratosphere to the troposphere and upper troposphere.

A review of elemental sulfur deposition in high sulfur-content natural gas transmission pipeline

High sulfur-content natural gas includes hydrogen sulfide, mercaptans, sulfoethers, and other sulfurous substances, with the major component being hydrogen sulfide. The development of high sulfur-content natural gas fields worldwide ensures the supply of not only clean energy, but also raw materials for industrial sulfur products. However, supersaturated precipitation of gaseous sulfur yields solid sulfur particles by nucleation, coagulation, and agglomeration with changing operation pressure, temperature, and species and concentration of gas components in high sulfur-content natural gas transmission pipelines. The solid particles will flow with the natural gas, and when the dynamic conditions for particle deposition are fulfilled, they will be deposited in pipeline. The deposition of solid sulfur particles will cause blockages in the transmission pipeline; furthermore, the elemental sulfur contacting the metal surface of the pipeline will cause electrochemical and chemical corrosion reactions. Eventually, the consequences of sulfur deposition in high sulfur-content natural gas transmission pipelines will cause serious hazards for pipeline operation and production. This paper summarizes the advances in the calculation of the sulfur gas-solid phase equilibrium, understanding of the growth and ablation kinetics mechanism of solid sulfur particles, and development of a gas-solid two-phase flow mathematical model. To fulfill the need for theory and experimental methods for predicting and preventing sulfur deposition in high sulfur-content natural gas transmission pipelines, the following three topics should be emphasized in future studies: First, limited experimental data is available on elemental sulfur solubility in sour gas at the pressure and temperature conditions of transmission pipelines, so sulfur solubility measurements should be established in the pressure and temperature range ( P ≤15.0 MPa, T ≤333.15 K) of transmission pipelines, considering the very low sulfur solubility under these conditions. Second, mathematical models of solid sulfur particle growth kinetics should be established based on molecular dynamics (MD) simulations with statistical mechanics and thermodynamics, combined with crystallization kinetics theory to determine nucleation, growth, and ablation behavior under the conditions of natural gas transmission pipelines. Third, mathematical models of the gas-solid two-phase flow in the transmission pipelines should be built considering the gas-solid phase change of elemental sulfur, and the growth and ablation of sulfur particles these models should involve the coupling effects of multiple parameters such as pipeline pressure, temperature, gas composition, and flow rate. These models could provide a quantitative description of elemental sulfur precipitation, sulfur particle growth, and particle flow behavior in high sulfur-content natural gas. Accordingly, the exact quantity and position of elemental sulfur deposition in high sulfur-content natural gas transmission pipelines can be predicted. These achievements will contribute to sulfur deposition prevention and improvement of control technology, as well as provide technical support for the design and management of high-sulfur natural gas transmission pipelines.

A 15-year record (2001–2015) of the ratio of nitrate to non-sea-salt sulfate in precipitation over East Asia

Abstract. Acidifying species in precipitation can have severe impacts on ecosystems. The chemical composition of precipitation is directly related to the amount of precipitation; accordingly, it is difficult to identify long-term variation in chemical concentrations. The ratio of the nitrate (NO3−) to non-sea-salt sulfate (nss-SO42−) concentration in precipitation on an equivalent basis (hereinafter, Ratio) is a useful index to investigate the relative contributions of these acidifying species. To identify the long-term record of acidifying species in precipitation over East Asia, the region with the highest emissions worldwide, we compiled ground-based observations of the chemical composition of precipitation over China, Korea, and Japan from 2001 to 2015 based on the Acid Deposition Monitoring Network in East Asia (EANET). The spatial coverage was limited, but additional monitoring data for Japan, southern China, and northern China around Beijing were utilized. The period of analysis was divided into three phases: Phase I (2001–2005), Phase II (2006–2010), and Phase III (2011–2015). The behaviors of NO3− and nss-SO42− concentrations and hence the Ratio in precipitation were related to these precursors. The anthropogenic NOx and SO2 emissions and the NOx ∕ SO2 emission ratio were analyzed. Further, satellite observations of the NO2 and SO2 column density to capture the variation in emissions were applied. We found that the long-term trend in the NO3− concentration in precipitation was not related to the variation in NOx emission and the NO2 column. In comparison, the nss-SO42− concentration in precipitation over China, Korea, and Japan was partially connected to the changes in SO2 emissions from China, but the trends were not significant. The long-term trends of Ratio over China, Korea, and Japan were nearly flat during Phase I, increased significantly during Phase II, and were essentially flat again during Phase III. This variation in Ratio in East Asia clearly corresponded to the NOx ∕ SO2 emission ratio and the NO2 ∕ SO2 column ratio in China. The initial flat trend during Phase I was due to increases in both NOx and SO2 emissions in China, the significantly increasing trend during Phase II was triggered by the increase in NOx emissions and decrease in SO2 emissions in China, and the return to a flat trend during Phase III was caused by declines in both NOx and SO2 emissions in China. These results suggest that emissions in China had a significant impact not only on China but also on downwind precipitation chemistry during the 15-year period of 2001–2015. In terms of wet deposition, the NO3− wet deposition over China, Korea, and Japan did not change dramatically, but the nss-SO42− wet deposition declined over China, Korea, and Japan from Phase II to III. These declines were caused by a strong decrease in the nss-SO42− concentration in precipitation accompanied by a reduction in SO2 emission from China, which counteracted the increase in precipitation. These findings indicated that the acidity of precipitation shifted from sulfur to nitrogen.

Impacts of SO2 gas impurity within a CO2 stream on reservoir rock of a CCS pilot site: Experimental and modelling approach

In order to evaluate chemical impacts of SO2 impurity on reservoir rock during CO2 capture and storage in deep saline aquifers, several batch reactor experiments were performed on laboratory scale using core rock samples from the pilot CO2 injection site in Heletz. In this experiment, the samples were exposed to pure N2(g), pure CO2(g), and CO2(g) with an impurity of 1.5% SO2(g) under reservoir conditions for pressure and temperature (14.5 MPa, 60 °C). Based on the set-up and the obtained experimental results, a batch chemical model was established using the numerical simulation program TOUGHREACT V3.0-OMP. Comparing laboratory and simulation data provides a better understanding of the rock-brine-gas interactions. In addition, it offers an evaluation of the capability of the model to predict chemical interactions in the target injection reservoir during exposure to pure and impure CO2. The best match between the geochemical model and experimental data was achieved when the reactive surface area of minerals in the model was adjusted in order to calibrate the kinetic rates of minerals. The simulations indicated that SO2(g) tends to dissolve rather quickly and oxidizes under a kinetic control. Hence, it has a stronger effect on the acidity of the brine than pure CO2(g) and as a result, increased mineral dissolution and caused the precipitation of sulfate and sulfide minerals. Ankerite, dolomite, and siderite, the most abundant carbonates in the sandstone rock sample, are subject to stronger dissolution in the presence of SO2 gas. The performed simulations confirmed a slower dissolution rate for ankerite and siderite than for dolomite. The model reproduced the precipitation of pyrite and anhydrite as observed in the laboratory. The dissolution of dolomite observed in the batch reaction test with pure N2 is assumed to be due to slight contamination with oxygen and modelling supported this. The inclusion of SO2 increased the porosity over that of the pure CO2 case, and is thus considered to increase the permeability and injectivity of the reservoir as well. Exposure to SO2 also increased the concentration of trace elements. The calibrated kinetic parameters determined in this study will be used to model the injection and long-term behavior of CO2 at the Heletz field site, and may be used for similar geologic reservoirs.

Flotation of carbon from a vanadium leaching residue of unroasted stone coal

The purpose of this study is to investigate the feasibility of carbon recovery through flotation from a vanadium leaching residue of unroasted stone coal. The flotation process was investigated by way of pH measurement, X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The washing-flotation test shows that some soluble substances in the residue inhibit coal flotation. The pH tests and dosage tests for sodium hydroxide and lime indicate that the precipitation of calcium sulphate in the pulp is disadvantageous to flotation. Besides, the sodium silicate is found to be beneficial to the flotation, and colloidal H4SiO4 is major active constituent in the pulp. Under optimal flotation conditions, a flotation concentrate was produced at a mass weight of 12.48%, with ash and combustible recovery products at 47.86% and 59.92%, respectively. Flotation is proved to have been an effective method for carbon recovery from vanadium leaching residues of unroasted stone coal. [Received: November 14, 2016; Accepted: May 10, 2017]

Health Consequences of Acid Rain in South West Sweden

Acid rain leads to loss of essential elements from soils and bedrock, causing an imbalance in especially dug well waters, as essential element concentrations decrease and potentially toxic element concentrations increase. In this study 72 private dug wells from acid regions (pH 7.0) in South-western Sweden. Women, drinking the water for at least 5 years, were interviewed about their health and water and hair samples were collected. The concentrations of about 40 elements in water and hair were analysed, mostly by ICP-MS. The concentrations of essential elements such as Ca, Cr, Mo, Se, K, and SO4 as well as the body’s buffering agent HCO3 were significantly lower in acid than in alkaline water. The median Ca concentration was 6 times lower in acid waters, and also in hair compared to alkaline. Median HCO3 was 14 times lower in acid waters. Mg was similar in both populations, since the Swedish bedrock in general has low Mg content, even so limestone in the alkaline area. The concentrations of especially Ca, Cr, HCO3 and SO4, peaked at pH 7.0 - 8.0, due to precipitation of carbonates and sulphates in alkaline soils and leaching from acid soils. The levels of toxic metals such as Cd and Pb were significantly higher in acid well water. High Cu concentration from pipes, causing especially diarrhoea, is a serious acidification problem. The contribution of essential elements to the daily intake from these well waters, 2 Litres consumption per day, was from 0% to above 30% for some elements, clearly showing that 10%, which is generally predicted, can be exceeded for people with private well waters, as well as provide 0%, which is the case for many acid well waters. Water elements were mirrored in hair, e.g. Ca and Mo. The loss of essential minerals, and increased concentration of toxic elements in acid well water, caused mineral imbalances in the body, as mirrored in hair. Women living in the acid area reported more negative health changes than women in the alkaline district, during the time they had been drinking their well water. The number of reported heart, intestinal, muscle, and skin problems were between 2 and 9 times higher among women drinking acid than alkaline well water.

Ecology and performance of aerobic granular sludge treating high-saline municipal wastewater.

The successful development of aerobic granular sludge (AGS) for secondary wastewater treatment has been linked to a dedicated anaerobic feeding phase, which enables key microbes such as poly-phosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms to gain a competitive advantage over floc-forming organisms. The application of AGS to treat high-saline sewage and its subsequent impacts on microbial ecology, however, are less well understood. In this study, the impacts of high-saline sewage on AGS development, performance and ecology were investigated using molecular microbiology methods. Two feeding strategies were compared at pilot scale: a full (100%) anaerobic feed; and a partial (33%) anaerobic feed. The results were compared to a neighbouring full-scale conventional activated sludge (CAS) system (100% aerobic). We observed that AGS developed under decreased anaerobic contact showed a comparable formation, stability and nitrogen removal performance to the 100% anaerobically fed system. Analysis of the microbial ecology showed that the altered anaerobic contact had minimal effect on the abundances of the functional nitrifying and denitrifying bacteria and Archaea; however, there were notable ecological differences when comparing different sized granules. In contrast to previous work, a large enrichment in PAOs in AGS was not observed in high-saline wastewater, which coincided with poor observed phosphate removal performance. Instead, AGS exhibited a substantial enrichment in sulfide-oxidising bacteria, which was complemented by elemental analysis that identified the presence of elemental sulfur precipitation. The potential role for these organisms in AGS treating high-saline wastewater is discussed.

Polysulfide Stabilization: A Pivotal Strategy to Achieve High Energy Density Li–S Batteries with Long Cycle Life

AbstractThe disproportionation of polysulfide (PS) is a long‐neglected and vital issue that causes the fast capacity fading of Li–S batteries. Based on the hard and soft acids and bases (HSAB) theory, a large size N‐methyl‐N‐ethyl pyrrolidinium (MEP+) cation is proposed to complex and stabilize the PS in electrolyte. The disproportionation of PS is successfully suppressed by this simple method, thereby avoiding the precipitation of sulfur in the electrolyte and reducing the loss of the active materials. The mutual interaction mechanism between MEP+ and Sn2− in electrolyte is comprehensively investigated and verified for the first time, via both density functional theory (DFT) calculation and experimental characterization. It enables the 5000 mA h Li–S batteries (soft package type) to achieve initial specific energy over 300 Wh kg−1 and maintain over 65% after 100 charge/discharge cycles at 1/20 C, while merely 24% is remained at 59 cycles without MEP+. This interesting finding is believed to shed light on the further development of Li–S batteries.

Development of atmospheric acid deposition in China from the 1990s to the 2010s

Atmospheric acid deposition is a global environmental issue. China has been experiencing serious acid deposition, which is anticipated to become more severe with the country's economic development and increasing consumption of fossil fuels in recent decades. We explored the spatiotemporal variations of acid deposition (wet acid deposition) and its influencing factors by collecting nationwide data on pH and concentrations of sulfate (SO42−) and nitrate (NO3−) in precipitation between 1980 and 2014 in China. Our results showed that average precipitation pH values were 4.59 and 4.70 in the 1990s and 2010s, respectively, suggesting that precipitation acid deposition in China has not seriously worsened. Average SO42− deposition declined from 40.54 to 34.87 kg S ha−1 yr−1 but average NO3− deposition increased from 4.44 to 7.73 kg N ha−1 yr−1. Specifically, the area of severe precipitation acid deposition in southern China has shrunk to some extent as a result of controlling the pollutant emissions; but the area of moderate precipitation acid deposition has expanded in northern China, associated with rapid industrial and transportation development. Furthermore, we found significant positive correlations between precipitation acid deposition, energy consumption, and rainfall. Our findings provide a relatively comprehensive evaluation of the spatiotemporal dynamics of precipitation acid deposition in China over past three decades, and confirm the idea that strategies implemented to save energy and control pollutant emissions in China have been effective in alleviating precipitation acid deposition. These findings might be used to demonstrate how developing countries could achieve economic development and environmental protection through the implementation of advanced technologies to reduce pollutant emissions.

Effect of sulphur deposition on well performance in a sour gas reservoir

AbstractSulphur deposition has been the centre of attention in sour gas reservoir development. While Roberts's solubility model is widely used in sour reservoir damage to describe elemental sulphur precipitation and deposition in a near‐wellbore area, this model cannot accurately predict a change in sulphur solubility. A productivity prediction model, with consideration of sulphur deposition, is also not complete, particularly for modelling sulphur deposition and fractured horizontal wells. In this study, based on the unsteady percolation mechanics theory and superposition principle, we develop a new numerical model to quantify fractured horizontal well production by combining various sulphur solubility models. We examine the effects of sulphur deposition on permeability, porosity, and production performance. The results show that sulphur deposition damages reservoirs and thus decreases well production in later stages. These results also show that the permeability and porosity reduction using Roberts's sulphur solubility model is greater than that using Hu et al.'s sulphur solubility model. The damage degree is relatively smaller when using Hu et al.'s sulphur solubility model, and the effect of sulphur deposition on a production performance curve is negligible. Moreover, Hu et al.'s model is closer to actual production data. The results can guide reservoir engineers to optimize development plans in sour gas reservoirs.

A prediction model for water breakthrough time in high-sulfur gas reservoir with edge water

The water coning phenomenon leads to decrease the wellhead pressure with moving of water into gas production zone, which is regarded as one of most serious problems during gas production. It has been shown that water breakthrough time plays an important role in analyzing the water coning phenomenon and production of water. However, the existing prediction models of water breakthrough time are very scarce and need to be discussed. In this work, a novel model for water breakthrough time in high-sulfur gas reservoir with edge water is developed based on flow law and sulfur precipitation model in porous media. The effect of irreducible water saturation, residual gas saturation, and the distance between gas well and edge water, sulfur saturation and gas non-Darcy flow on water breakthrough time was involved in this model. The validity of the proposed model is verified by comparing the existing models available. A good trend is found between them. In addition, the influence of the distance between gas well and edge water, sulfur saturation and gas non-Darcy flow on water breakthrough time was detail discussed further.