MINTEQ Software Research Articles

The role of chloride in calcium precipitation from drinking groundwater

AbstractBACKGROUNDChloride is present in many water sources. In addition, the use of hypochlorite as a disinfectant for drinking water increases its chloride concentration. However, the effect of this prevalent ion on Ca precipitation in drinking water is poorly described, and its effect, as a function of the Ca/Mg ratio, which drives Ca precipitation, has not been studied. Accordingly, Ca precipitation was studied using batch assays at different concentrations of chloride and hypochlorite for Ca/Mg ratios of 4.0 and 1.1. The assays were performed at 20 and 25 °C. Chemical speciation analysis was performed using Visual MINTEQ software, and precipitates derived from the process were analyzed by X‐ray diffraction.RESULTSCa precipitation was influenced by the Cl− concentration, causing an oversaturation of CaCO3 with a trend to a maximum. The highest Ca precipitation was achieved at a Ca/Mg ratio of 4.0, obtained at an initial Cl− concentration of 50 mg L−1, both at 20 and 25 °C. For a Ca/Mg ratio of 1.1, the highest precipitation occurred at initial Cl− concentrations of 10–15 mg L−1 at 20 °C and 20 mg L−1 at 25 °C. In ClO− experiments, Ca precipitation increases proportionally with hypochlorite dosage. Greater Ca precipitation is observed at Ca/Mg = 4.0 compared to Ca/Mg = 1.1. The proportion of aragonite or calcite in the precipitates obtained depends on the presence of Cl− and ClO− as well as on the Ca/Mg ratio.CONCLUSIONChloride affects Ca precipitation by oversaturation, and the precipitation of CaCO3 species depends on the concentration of Mg. © 2024 Society of Chemical Industry (SCI).

Highly efficient recovery of phosphate and fluoride from phosphogypsum leachate: Selective precipitation and adsorption

Phosphogypsum, a typical by-product in the phosphorus chemical industry, could generate a large amount of leachate containing phosphate and fluoride in the process of rainfall and long-term stacking, which not only causes serious environmental pollution, but also leads to a waste of resources. In this study, a united treatment of calcium hydroxide precipitation and lanthanum zeolite (La-ZFA) adsorption was proposed to achieve the recovery of phosphate and fluoride from phosphogypsum leachate. In phosphogypsum, most phosphorus could be leached except P in the residual occurrence form, while for fluoride, only water-soluble F could be effectively leached. The optimum leaching amounts of phosphate and fluoride were 22.59 and 4.64mg/g, respectively, at liquid-solid ratio of 400:1, leaching time of 120min, pH of 6.0, particle size of >200 mesh (<0.075mm), and leaching temperature of 25°C. Using Ca(OH)2 as the precipitant, the phosphate could be precipitated selectively from phosphogypsum leachate by controlling pH and time, and the concentrations of it decreased significantly to 0.29mg/L at pH 10.0, with a removal efficiency of 99.48%. XRD, SEM and Visual MINTEQ software analysis proved that the main component of the precipitate was hydroxyapatite (Ca5(PO4)3(OH)). After P precipitation, a series of sorbents for fluoride were investigated, and La-ZFA sorbent was chosen and utilized to recover the fluoride from the leachate through a cyclic fixed-bed column. The efficiency of La-ZFA was basically not affected by the high concentration sulfate, and it can selectively adsorb fluoride from phosphogypsum leachate, leading to a final fluoride concentration of 0.29mg/L in the effluent. The characterization demonstrated that fluoride might be adsorbed onto the La-ZFA via ligand exchange with hydroxy groups. The proposed method in this study is expected to sequentially recover phosphate and fluorine from the leachate of phosphogypsum, and it has great guiding significance for resource utilization and management of phosphogypsum.

Remediation characteristics and effects of electrokinetic-citric acid system on karst soil contaminated by arsenic and cadmium

Remediation characteristics and effects of electrokinetic-citric acid system on karst soil contaminated by arsenic and cadmium

Comparison of Solubilization Treatment Technologies for Phosphorus Release from Anaerobic Digestate of Livestock Manure

This study addresses the imminent threat of phosphorus (P) depletion, investigating anaerobically digested livestock manure as a high-concentration P alternative. To achieve this objective, Visual MINTEQ software, a general-purpose software used for chemical equilibrium modeling, was employed to simulate the alteration in P species fractions at different pH levels. The investigation further examined the variation in P release rates and electrical energy consumption across various pretreatment processes as influenced by pH levels. The results indicate a significant pH influence on P release, with enhanced efficacy under both acidic and alkaline conditions. At pH 2, total P concentration peaked at 684 mg·L−1, with 83.0% reactive P, in contrast with pH 10 conditions, which exhibited 504 mg·L−1 and 48.4%, respectively. P release increased with reaction time across all pretreatment processes. Sonication notably increased P release by 126.9%, with the highest reactive P release efficiency at 2.09 mg·L−1·Wh−1, emerging as an optimal process. Simulation results using Visual MINTEQ software indicate that the inclination for P release in alkaline conditions can be ascribed to the heightened presence of hydroxyapatite, brushite, and Ca-Fe (III)-phosphate bonds with rising pH levels. These simulation results, which are consistent with the experimental results, affirm the crucial influence of cations in determining P release on pH values.

Fractionation and speciation of metals in lakes formed by abandoned clay pits from industrial effluents (Santa Gertrudes, São Paulo, Brazil) using the diffusive gradient in thin films (DGT) technique

Environmental impacts caused by mining activities (mainly tailings and effluents) are presenting serious challenges for humanity worldwide. In Brazil, clay extraction activities in the Ceramic District of Santa Gertrudes (CDSG) have led to the formation of abandoned drainage wells causing environmental and human health concerns. In the 90's, it was discovered that in one of the production areas, known as the region of the lakes of Santa Gertrudes, several ceramic industries had contaminated lakes created by abandoned clay pits with industrial effluents containing toxic metals. In the present study, analysis of total and dissolved concentrations of Al, Cd, Co, Cu, Mn, Ni, Pb and Zn in the waters of these lakes were combined with the diffusive gradients in thin films (DGT) technique to assess the lability and bioavailability of the target elements, representing one of the first studies to investigate the real environmental impact of contamination caused by ceramic production wastes to an aquatic system. Furthermore, based on the total concentrations and main physicochemical characteristics of each lake, a speciation analysis was performed using the MINTEQ software which data was compared with other surface water systems. The results indicated the presence of metals associated with ceramic residues in total, dissolved and labile fractions. It was verified that Zn, Ni and Cu were the only target metals found in labile form and according to speciation were present in the form of "free" ions, and thus may present risk in terms of bioavailability, although the majority of the total concentrations are within the limits established by the national environmental agency.

Electroplating wastewater treatment by in-situ formation of organic anions and inorganic anions intercalated layered double hydroxides

The electroplating wastewater containing various metal ions was treated by adding sodium dodecyl benzene sulfonate (SDBS) and regulating pH value, and the resulting precipitates were characterized by X-ray diffraction (XRD). The results showed that organic anions intercalated layered double hydroxides (OLDHs) and inorganic anions intercalated layered double hydroxides (ILDHs) were in-situ formed to remove heavy metals during the treatment process. In order to reveal the formation mechanism of the precipitates, SDB- intercalated Ni-Fe OLDHs, NO3- intercalated Ni-Fe ILDHs and Fe3+-DBS complexes were synthsized by co-precipitation at various pH values for comparison. These samples were characterized by XRD, Fourier Transform infrared (FTIR), element analysis as well as the aqueous residual concentrations of Ni2+ and Fe3+ were detected. The results showed that OLDHs with good crystal structures can be formed as pH≤7, while ILDHs began to form at pH=8. When pH<7, complexes of Fe3+ and organic anions with the ordered layered structure were formed firstly, and then with increase in pH value, Ni2+ inserted into the solid complex and the OLDHs began to form. However, Ni-Fe ILDHs were not formed when pH≤7. The Ksp (Solubility Product Constant) of OLDHs was calculated to be 3.24×10-19 and that of ILDHs was 2.98×10-18at pH=8, which suggested that OLDHs might be easier to form than ILDHs. The formation process of ILDHs and OLDHs were also simulated through MINTEQ software, and the simulation output verified that OLDHs could be easier to form than ILDHs at pH≤7. Information from this study provides a theoretical basis for effective in-situ formation of OLDHs in wastewater treatment.

Predicting chemical speciation of metals in soil using Visual Minteq

• Soil processes affect metal chemical speciation and their biogeochemical activity. • The current study predicted chemical speciation of eight metals in two soil layers. • Divalent forms of metals predominated in both soil layers (79.9%). • Chromium showed a chemical speciation that varied from that of the other metals (95.8% as CrOH+). • Mean percentage ages of all metal ions were similar for all 15 field locations investigated. From soil contamination and risk assessment perspectives, it is imperative to understand the ecological processes occurring in soils. Certain soil processes greatly affect chemical speciation of potentially toxic metals (PTMs), and thus also influence their biogeochemical activity. The current study analyzed chemical speciation of eight PTMs (Cd, Cr, Fe, Cu, Mn, Ni, Zn, and Pb) in upper and lower soil layers for 15 agronomic fields of Vehari-Pakistan using Visual Minteq software. The divalent forms of most PTMs (PTM2+) generally predominated in both soil layers (79.9% overall occurrence). However, chromium revealed a different pattern of chemical speciation (95.8% as CrOH+) compared to other PTMs. The mean percentage of all the PTMs2+ was slightly higher for the lower soil layer (81.3%) than in the upper layer (78.4%), the trend being same for all the PTMs, except Cr. This higher PTMs2+ percentage in lower soil layers than upper layers was due to lower content of organic matter and other anions such as Cl− and HCO 3 − . The mean percentage ages of all the PTMs2+ was similar among all the 15 agronomic fields, which was confirmed by strong Pearson correlation values (R2 > 0.95). The PCA graph grouped all the agronomic fields and PTM2+ closely, except Cr2+ and Cu2+. This grouping confirmed the similar chemical speciation of PTMs, except Cu and Cr in studied fields.

Controlling reactions during heavy metal leaching from municipal solid waste incineration fly ash

This research aimed to characterize the physical and chemical properties of municipal solid waste (MSW) incineration fly ash, as well as to investigate the leaching of heavy metals during toxicity characteristics leaching procedure (TCLP) process. To understand the leaching behaviour, concentrations of heavy metals, chloride, sulphate and calcium at various leaching, time was monitored together with pH of the leaching solution. Results showed that the chemical compositions of fly ashes led to differences in leaching environment. For the two fly ashes under study, one resulted in a leaching environment with pH of 10?12 while the other had pH about 6?7. Based on pH, anions and cations concentrations, Minteq software was employed to investigate the speciation of heavy metals. Results showed that the shift in precipitation/dissolution balance of carbonate and hydroxides of heavy metals could explain the fluctuation in metal concentrations during the leaching process, which indicates that leaching was probably controlled by these reactions. On the other hand, addition of EDTA changed the controlling reactions. Chelating reactions between heavy metals and EDTA led to much higher leaching toxicity due to the presence of heavy metals, showing that the presence of chelating organics in natural environment may facilitate heavy metal leaching.

Content and Speciation of Phosphorus in Lake Kórnickie

This paper presents the speciation of phosphorus in bottom sediments and its spatial variability in Lake Kórnickie. This study provides a quantitative determination of the abundance and chemical speciation of P and potential P-release rates from Lake Kórnickie. Phosphorus (P) is an important macronutrient that can limit primary productivity in fresh water ecosystems. The study was conducted during the hydrological years 2016–2018. The speciation analysis was carried out using Visual Minteq software. The predominant form of orthophosphate (V) in the waters of Lake Kórnickie was the HPO42− anion, which was related to the reaction of the studied waters. Conditions favoring the precipitation of orthophosphates to hydroxyapatite, aragonite, and calcite prevailed in the lake waters. No cyclic periods of deposition of minerals and release of phosphorus from bottom sediments were observed and, for most of the study period, the lake acted as a “trap” for phosphorus at point JK1. The findings of this study suggest that the internal sedimentary P loading contributes substantial bioavailable P to the water column at one of sampling points (JK2). The accumulation of phosphorus in bottom sediments meant that the lake restoration processes carried out in various lakes may not have had the intended results. At the same time, bottom sediments can be a secondary source of pollution of river waters with this element despite the reduction of inflow from the catchment area of this element.

Separation of calcium chloride from waste acidic raffinate in HCl wet process for phosphoric acid manufacture: Simulated and experimental study

Phosphoric acid manufacture by HCl wet process is a phosphogypsum-free route, which is promising for replacing traditional H2SO4 wet process. However, large amount of CaCl2-containing acidic raffinate was discharged after solvent extraction of H3PO4. In this study, pure CaCl2·2H2O was recovered from the raffinate. The ionic forms and residual amount changes with the pH rise in the raffinate was first simulated by Visual MINTEQ software, and found the precipitation for the components was in the following sequential order of Si>F>P>Al>Cr>Pb≈Mg. Based on the calculation, one-step and multi-steps neutralization processes were designed for separation of impurities. Feed grade calcium hydrophosphate can be separated from the raffinate by multi-steps neutralization. A well-crystallized CaCl2·2H2O assaying 98.9 wt% was obtained after evaporative crystallization of the fluorine-depleted solution. Combined with our previous studies on the phosphate ore digestion and H3PO4 solvent extraction, a complete HCl wet process for H3PO4 manufacture was established.

Effects of Bacterial Culture and Calcium Source Addition on Lead and Copper Remediation Using Bioinspired Calcium Carbonate Precipitation.

Lead and copper ions from wastewater induced by metallurgical processes are accumulated in soils, threatening plant and human health. The bioinspired calcium carbonate precipitation is proven effective in improving the cementation between soil particles. However, studies on capsulizing heavy metal ions using the bioinspired calcium carbonate precipitation are remarkably limited. The present study conducted a series of test tube experiments to investigate the effects of bacterial culture and calcium source addition on the remediation efficiency against lead and copper ions. The calcium carbonate precipitation was reproduced using the Visual MINTEQ software package to reveal the mechanism affecting the remediation efficiency. The degradation in the remediation efficiency against lead ions relies mainly upon the degree of urea hydrolysis. However, higher degrees of urea hydrolysis cause remediation efficiency against copper ions to reduce to zero. Such high degree of urea hydrolysis turns pH surrounding conditions into highly alkaline environments. Therefore, pursuing higher degrees of urea hydrolysis might not be the most crucial factor while remedying copper ions. The findings shed light on the importance of modifying pH surrounding conditions in capsulizing copper ions using the bioinspired calcium carbonate precipitation.

Effects of the Urease Concentration and Calcium Source on Enzyme-Induced Carbonate Precipitation for Lead Remediation.

Heavy metal contamination during the rapid urbanization process in recent decades has notably impacted our fragile environments and threatens human health. However, traditional remediation approaches are considered time-consuming and costly, and the effect sometimes does not meet the requirements expected. The present study conducted test tube experiments to reproduce enzyme-induced carbonate precipitation applied to lead remediation under the effects of urease concentration and a calcium source. Furthermore, the speciation and sequence of the carbonate precipitation were simulated using the Visual MINTEQ software package. The results indicated that higher urease concentrations can assure the availability of CO3 2− during the enzyme-induced carbonate precipitation (EICP) process toward benefiting carbonate precipitation. The calcium source determines the speciation of carbonate precipitation and subsequently the Pb remediation efficiency. The use of CaO results in the dissolution of Pb(OH)2 and, therefore, discharges Pb ions, causing some difficulty in forming the multi-layer structure of carbonate precipitation and degrading Pb remediation. The findings of this study are useful in widening the horizon of applications of the enzyme-induced carbonate precipitation technology to heavy metal remediation.

Effect of chloride concentration on the cytotoxicity, bioavailability, and bioreactivity of copper and silver in the rainbow trout gut cell line, RTgutGC.

Chloride (Cl-) influences the bioavailability and toxicity of metals in fish, but the mechanisms by which it influences these processes is poorly understood. Here, we investigated the effect of chloride on the cytotoxicity, bioavailability (i.e., accumulation) and bioreactivity (i.e., induction of mRNA levels of metal responsive genes) of copper (Cu) and silver (Ag) in the rainbow trout gut cell line (RTgutGC). Cells were exposed to metals in media with varying Cl- concentrations (0, 1, 5 and 146 mM). Metal speciation in exposure medium was analyzed using Visual MINTEQ software. Cytotoxicity of AgNO3 and CuSO4 was measured based on two endpoints: metabolic activity and membrane integrity. Cells were exposed to 500 nM of AgNO3 and CuSO4 for 24 h in respective media to determine metal bioavailability and bioreactivity. Ag speciation changes from free ionic (Ag+) to neutral (AgCl), to negatively charged chloride complexes (AgCl2-, AgCl3-) with increasing Cl- concentration in exposure media whereas Cu speciation remains in two forms (Cu2+ and CuHPO4) across all media. Chloride does not affect Ag bioavailability but decreases metal toxicity and bioreactivity. Cells exposed to Ag expressed significantly higher metallothionein mRNA levels in low Cl- media (0, 1, and 5 mM) than in high Cl- medium (146 mM). This suggests that chloride complexation reduces silver bioreactivity and toxicity. Conversely, Cu bioavailability and toxicity were higher in the high chloride medium (146 mM) than in the low Cl- (0, 1, and 5 mM) media, supporting the hypothesis that Cu uptake may occur via a chloride dependent mechanism. CLINICAL TRIALS REGISTRATION: This study did not require clinical trial registration.

Bioavailability of heavy metals in the soil of Doustbaglu region (Meshginshahr) and determining toxic species by sequential extraction and Visual Minteq software

سابقه و هدف:: اکسیداسیون زون­ های کانی سازی شده سولفیددار طی فرایند هوازدگی در اثر واکنش­ های بیولوژیکی و شیمیایی تشدید شده و زهاب اسیدی1 حاصل سبب آزادسازی و تحرک عنصرهای فلزی سمی و سنگین از سنگ مادر و تمرکز آن‌ها در محیط خاک یا آب می‌شود. در این پژوهش، نمونه­ های خاک برداشته شده از اطراف روستای دوست­ بگلو (شمال­ غرب مشگین­ شهر) که یک منطقه کانه ­زایی و دگرسانی است، مورد بررسی قرار گرفت و گونه ­های شیمیایی، میزان مسمومیت ­زایی و منشأ عنصرهای سنگین As، Cd، Cu، Cr، Pb، Sb، Ni و Zn تعیین گردید.مواد و روش ­ها: در این پژوهش، غلظت کل و زیست دسترس‌پذیری عنصرهای سنگین As، Cd، Cu، Cr، Pb، Sb، Ni و Zn در 5 نمونه خاک سطحی توسط گونه بندی به روش استخراج ترتیبی (تسیر) در پنج فاز (تبادل پذیر، متصل به کربنات، متصل به اکسیدهای آهن و منگنز، متصل به مواد آلی و فاز باقیمانده) و نرم افزار ترمودینامیکی Visual Minteq مورد ارزیابی واقع شد.نتایج و بحث: نتایج حاصل از روش استخراج ترتیبی معلوم می ­کند که بیشترین غلظت از مجموع غلظت کل هر 8 عنصر سنگین مورد مطالعه در فاز باقی­مانده (تثبیت شده در ساختار کانی­ ها) قرار دارد. این مسئله نشان دهنده منشأ زمین­ زاد این عنصرها بوده و می­ تواند حاصل فرسایش و هوازدگی سنگ ­های منطقه در نظر گرفته شود. عنصر Sb در قیاس با دیگر عنصرها مورد بررسی غلظت بیشتری در فازهای بالقوه دسترس ­پذیر (تبادل­ پذیر، متصل به کربنات، متصل به اکسیدهای آهن و منگنز و متصل به مواد آلی) داشته و احتمال مسمومیت ­زایی این عنصر بیشتر است. خروجی نرم افزار نشان داد که در نمونه‌های بیان شده گونه­ های غالب سرب به­ صورت Pb(SO4)22-، Pb2+ و PbSO4 (aq)، مس به ­صورت CuSO4 (aq) وCu2+ نیکل به ­صورت NiSO4(aq)، Ni2+ و NiSO4، آنتیموان به­ صورت Sb(OH)3، Sb(OH)2+ و Sb(OH)61-، به ­صورت روی Zn(SO4)22-، ZnSO4 (aq) و Zn2+، آرسنیک به ­صورت H3AsO3 و H2AsO4- کادمیوم به­ صورت Cd(SO4)22- و Cd2+ و گونه ­های غالب کروم به ­صورت CrSO4+، CrOHSO4 (aq) و HCrO4- حضور داشتند. عموماً گونه‌های آبگین آزاد عنصرهای بیان شده قابلیت تحرک بیشتری نسبت به گونه‌های دیگر دارند، در عوض غلظت این گونه‌ها در مقایسه بسیار اندک است و بیشتر این عنصرها، بیشتر در قالب کمپلکس‌هایی با تحرک ­پذیری کم حضور دارند.نتیجه گیری: براساس نتایج استخراج ترتیبی؛ هر 8 عنصر مورد مطالعه، پتانسیل ریسک اکولوژیکی بالا و رخداد آلودگی قابل توجه در رسوب آبراهه و افق­ های سطحی خاک زراعی منطقه دوست بگلو را نشان می ­دهد. تحلیل یافته ­های نرم افزار Visual Minteq گویای آن است که فعال­ترین گونه‌های این عنصرها و غلظت مربوطه بین تمام انواع گونه‌های محتمل به ­ترتیب شامل: Cd2+ (49/1%)، CrOHSO4 (aq) (20/25%)، Cu2+ (38/%10)، Pb2+ (37/%1)، ZnSO4 (aq (83/18%) می ­باشد. از آنجایی که گونه‌های متحرک‌تر، غلظت پایینی داشته و از طرفی بنابر نتایج استخراج ترتیبی بیشترین مقدار عنصرهای مورد مطالعه در فاز باقیمانده حضور دارند، بنابراین میزان زیست دسترس پذیری و مسمومیت زایی این عنصرها ناچیز برآورد می ­شود. در حالت کلی می­ توان نتیجه گیری کرد که تنها درصد اندکی از عنصرها در فازهای زیست دسترس پذیر حضور دارند و نگرانی درباره احتمال تحرک عنصرها با تغییر شرایط محیطی و دسترس­پذیری برای گیاهان را از بین می­ برد.

The Effect of Calcium Source on Pb and Cu Remediation Using Enzyme-Induced Carbonate Precipitation.

Heavy metal contamination not only causes threat to human health but also raises sustainable development concerns. The use of traditional methods to remediate heavy metal contamination is however time-consuming, and the remediation efficiency may not meet the requirements as expected. The present study conducted a series of test tube experiments to investigate the effect of calcium source on the lead and copper removals. In addition to the test tube experiments, numerical simulations were performed using Visual MINTEQ software package considering different degrees of urea hydrolysis derived from the experiments. The remediation efficiency degrades when NH4 + and OH− concentrations are not sufficient to precipitate the majority of Pb2+ and Cu2+. It also degrades when CaO turns pH into highly alkaline conditions. The numerical simulations do not take the dissolution of precipitation into account and therefore overestimate the remediation efficiency when subjected to lower Pb(NO3)2 or Cu(NO3)2 concentrations. The findings highlight the potential of applying the enzyme-induced carbonate precipitation to lead and copper remediations.

Parametric study and speciation analysis of rare earth precipitation using oxalic acid in a chloride solution system

Oxalic acid precipitation is a common step in the purification of rare earth elements (REE) from a concentrated pregnant leach solution (PLS). However, the presence of contaminants such as Al, Fe, and Ca in given amounts decreases the REE precipitation efficiency and product purity while also increasing the amount of oxalic acid needed to maximize recovery. As such, a statistically designed test program was performed to identify the optimal conditions necessary for a relatively low REE content PLS containing elevated concentrations of contaminant ions. The performance objective was maximization of REE precipitation efficiency while minimizing the oxalic acid dosage. A central composite design was utilized to quantify performance impacts and identify the ultimate set of parameter values for oxalic acid dosage, Fe(III) contamination concentration, solution pH, and reaction temperature. The resultant model suggested that oxalic acid dosage and reaction pH are the most significant factors for the REE precipitation efficiency, followed by the interaction of oxalic dosage and Fe concentration. Test results indicate that increasing the oxalic acid concentration from 0 g/L to 80 g/L improved the REE precipitation efficiency from approximately 4.2% to 95.0%. Furthermore, raising the solution pH from 0.5 to 2.5 considerably enhanced the precipitation efficiency from 0.0% to 98.9%. A solution temperature elevation decreased REE recovery, which indicated an exothermic reaction between REEs and oxalate anions. Finally, a high level of Fe contamination adversely impacted REE precipitation efficiency. To further the understanding of the REE-oxalate system, a fundamental solution chemistry study was performed using the equilibrium constants of the reactions. The study resulted in the development of oxalate speciation diagrams and provided an analysis of the REE precipitation characteristics at various oxalate anion concentrations and Fe(III) contamination levels using MINTEQ software. The dominant Fe(III) species in the solution system were found to be Fe-(C2O4)33-, Fe-(C2O4)2-, and Fe-(C2O4)+, which consume the majority of the oxalate anions. The simulated model was found to be in agreement with the experimental findings and helped to explain the adverse impact of increased iron concentrations on REE precipitation efficiency.

Flooding-induced inorganic phosphorus transformations in two soils, with and without gypsum amendment.

Anaerobic conditions developed during flooding can increase phosphorus (P) losses from soils to waterways. Soil amendment with gypsum (CaSO4 ·2H2 O) can effectively reduce flooding-induced P release, but its effectiveness is soil dependent, and the reasons are poorly understood. The objectives of this study were to reveal the possible inorganic P transformations during flooding of two soils (acidic-Neuenberg sandy loam [NBG-SL] and alkaline-Fyala clay [FYL-Cl]), with and without gypsum amendment prior to flooding. Porewater samples collected at 0, 35, and 70 d after flooding (DAF) from soils incubated in vessels were analyzed for dissolved reactive P (DRP); pH; and concentrations of calcium (Ca), magnesium, iron (Fe), manganese, chloride, nitrate, sulfate, and fluoride. Thermodynamic modeling using Visual MINTEQ software and chemical fractionation of soil P were used to infer P transformations. Soil redox potential (Eh) decreased with flooding and favored reductive dissolution of Fe-associated P increasing porewater DRP concentrations. Greater solubility of Ca-P under acidic pH maintained a higher DRP concentration in NBG-SL during early stages of flooding. A subsequent increase in pH with flooding and higher Ca concentration with added gypsum enhanced the stability of Ca-P (β-tricalcium phosphate and octacalcium phosphate), reducing the DRP concentration in gypsum-amended NBG-SL. Stability of Ca-P was less affected with flooding and gypsum amendment in FYL-Cl soil because it had an alkaline pH and inherently higher Ca concentration. The FYL-Cl, with a more rapid decrease in Eh than NBG-SL, became severely reduced, releasing more P and Fe by 70 DAF. These conditions favored vivianite formation in FYL-Cl but not in NBG-SL.

Effects of bacterial inoculation and calcium source on microbial-induced carbonate precipitation for lead remediation

Heavy metal contamination has caused serious threats to surrounding fragile environments and human health. While the novel microbial-induced carbonate precipitation (MICP) technology in the recent years has been proven effective in improving material mechanical and durability properties, the mechanisms remedying heavy metal contamination still remain unclear. In this study, the potential of applying the MICP technology to the lead remediation under the effects of urease activity and calcium source was explored. The values of OD600 corresponding to the ureolytic bacterial activity, electrical conductivity (EC), urease activity (UA) and pH were applied to monitor the degree of urea hydrolysis. Further, the carbonate precipitations that possess different speciations and cannot be distinguished through test tube experiments were reproduced using the Visual MINTEQ software package towards verifying the validity of the proposed simulations, and revealing the mechanisms affecting the lead remediation efficiency. The findings summarised in this work give deep insights into lead-contaminated site remediation engineering.

Bioaccumulation characteristics and acute toxicity of uranium in Hydrodictyon reticulatum: An algae with potential for wastewater remediation

The bioaccumulation characteristics and acute toxicity of uranium (U) to Hydrodictyon reticulatum were studied to provide reference for further mechanism and application research. According to an analysis using visual MINTEQ software, the pH change caused by the photosynthesis of H. reticulatum leads to U remaining mainly in the species of UO2(OH)3-. Fourier transform infrared spectrometer (FTIR) and transmission electron microscope (TEM) analysis showed that the bioaccumulation of U was related to the amino and carboxyl groups, resulting in cell wall damage. Using innovative cell staining microscopic observation techniques, U was mainly compartmentalized in vacuoles and pyrenoid; chlorophyll, soluble protein, dehydrogenase activity, and other physiological responses were closely related to the U stress concentration. Especially here, the change trend of the specific activity and specific growth rate of dehydrogenase was consistent, showing low concentration promotion and high concentration inhibition. Combined with the toxic response of the two, the half inhibitory dose for 72h was determined to be about 30mgL-1. When bioaccumulation equilibrium is reached at 72h, the maximum tolerance concentration of U without affecting the easy collection characteristics of the algae is 30mgL-1, and the maximum U bioaccumulation capacity was able to reach 24.47±0.86mgg-1 by dry biomass.

Recycling the steel pickling waste liquor to produce a low-cost material for immobilization of heavy metal(loid)s

This work aims to demonstrate the practicability of employing Iron (Fe)-manganese (Mn) binary oxide (FMBO) synthesized from pickling wastewater to immobilize arsenic (As(V)) and antimony (Sb(V)). Visual MINTEQ software was used to simulate the speciation of As(V) and Sb(V) under different pH values. The adsorption performance of FMBO for Sb(V) and As(V) were examined by batch experiments, the pH impact, sorption kinetics, sorption isotherms and the reuse of the adsorbent were investigated. The pH impact results demonstrated that the absorption capacity decreased dramatically as the pH value increased, the maximum adsorption capacities As(V) and Sb(V) were obtained at pH value of 4 as 95.24 and 147.1 mg/g, respectively. The kinetic results indicated that the pseudo-second order model could fit the kinetic data of Sb(V) and As(V) well. Equilibrium studies displayed that the adsorption of Sb(V) and As(V) on FMBO could be appropriately described by Freundlich model. Results of the binary adsorption indicated that Sb(V) exhibited ∼ 5% improvement for As(V) when the initial Sb(V) content raised from 0 to 500 mg/L, while As(V) showed a significant hindrance for Sb(V) adsorption. Moreover, utilization of FMBO could also effectively reduce the TCLP extractable and easy mobile As and Sb in contaminated soil, thus reducing their bioavailability. In view of the advantages of cost-effective, eco-friendly and excellent sorption performance, the steel pickling waste liquor-derived FMBO could be regarded as a promising amendment for remediating As and Sb contamination in environment. • A new low-cost adsorbent (FMBO) was prepared from steel pickling waste liquor. • FMBO exhibited an excellent performance for sorption of As(V) and Sb(V). • The existence of Sb(V) favor As(V) sorption, while As(V) showed opposite effect on Sb(V). • The FMBO could also effectively reduce the bioavailability of soil As and Sb.