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In this study, we studied the degradation kinetics of a common iodine contrast agent, diatrizoate, by ozone and the formation of disinfection by-products (DBPs) in the sequential chlorination. Effects of ozone concentration, solution pH, and bromide concentration on diatrizoate degradation were evaluated. The results indicate that diatrizoate can be effectively degraded (over 80% within 1 h) by ozone, and the degradation kinetics can be well described using the pseudo-first-order kinetic model. The pseudo-first-order rate constant (kobs) of diatrizoate degradation significantly increased with increasing ozone concentration and decreasing bromide concentration. The kobs kept increasing with the increase of pH value and reached a maximum of 6.5 (±0.05) × 10−2 min−1 at pH 9. As the ozone concentration gradually increased from 0.342 to 1.316 mg/L, the corresponding kobs of diatrizoate degradation increased from 1.76 (±0.20) × 10−3 to 4.22 (±0.3) × 10−2 min−1. The bromide concentration exhibited a strong inhibitory effect on diatrizoate degradation because of the competition for ozone with diatrizoate. Trichloromethane was the only detected DBP in the subsequent chlorination in the absence of bromide. However, in the presence of bromide, six other DBPs were detected, and bromochloroiodomethane and tribromomethane became the major products with concentrations 1–2 orders higher than those of the other DBPs. In order to provide safe drinking water to the public, water should be maintained at circumneutral pH values and low bromine concentrations ( 7.; •OH played a major role in diatrizoate degradation during ozonation.; Bromide can strongly inhibit diatrizoate degradation because of the competition for ozone with diatrizoate.; The formation of DBPs can be controlled at circumneutral pH and low bromine concentrations (

The transformation behavior of ferrous sulfate was examined during hematite precipitation for iron removal in hydrometallurgical zinc. Specifically, the effects of the method used for oxygen supply (pre-crystallization or pre-oxidation of ferrous sulfate) and temperature (170–190 °C) on the redissolution and oxidation–hydrolysis of ferrous sulfate were studied. The precipitation characteristics and phase characterization of the hematite product were investigated. The results showed that the solubility of ferrous sulfate was considerably lower at elevated temperatures. The dissolution behavior of ferrous sulfate crystals was influenced by both the concentrations of free acid and zinc sulfate and the oxydrolysis of ferrous ions. Rapid oxydrolysis of ferrous ions may serve as the dissolution driving force. Hematite precipitation proceeded via the following sequential steps: crystallization, redissolution, oxidation, and precipitation of ferrous sulfate. The dissolution of ferrous sulfate was slow, which helped to maintain a low supersaturation environment, thereby affording the production of high-grade hematite.

In this study, the degradation kinetic model and pathways of a UV filter, 2-phenylbenzimidazole-5-sulfonic acid (PBSA) during UV/chlorination were investigated. PBSA hardly degraded under UV irradiation or chlorination alone, but its degradation in UV/chlorination was efficient and followed pseudo-first order kinetics at pH 7. Increasing the chlorine dosage from 12.5 to 200 μM can enhance PBSA degradation, while increasing pH from 5 to 9 caused opposite effect. The second-order rate constants between radicals (∙Cl, ∙ClO, and ∙OH) and PBSA and the contribution of ∙OH during UV/chlorination were determined. ∙Cl and ∙OH were confirmed to be the main contributors to PBSA degradation. The presence of background [Formula: see text] and humic acid can inhibit PBSA degradation, but the presence of Cl

Stone coal is a kind of carbonaceous shale that contains vanadium. The sequential chemical extractions were adopted to analyze the vanadium phases of stone coal and its combustion fly ash. The results showed that the vanadium in stone coal mainly consisted in aluminosilicate. The vanadium in fly ash mainly existed in organic matter, aluminosilicate and Fe–Mn oxides, and the other vanadium existed in exchangeable fraction. Through the burning process, the vanadium was released and enriched in fly ash. Because of particular vanadium migration behaviors, the distribution of vanadium in phases became more scattered, and the leaching of vanadium in fly ash was easier than that in stone coal.

Prometryn is a herbicide that is widely used and frequently detected in aqueous environment and soil. Prometryn is chemically stable, biologically toxic, and easily to accumulate in living bodies, which can cause accumulate in the environment and acute and chronic toxicity to living creatures. In this study, factors affecting the degradation kinetics of prometryn chlorination were studied, including solution pH, bromide and ammonium concentrations, and temperature. Prometryn reacted quickly with aqueous chlorine following the pseudo-first-order kinetics. The maximum pseudo-first-order rate constant (kapp) appeared at pH 5 with the observed rate constant (kobs) as 190. 08 h−1; the minimum value of kapp reached at pH 9 with kobs as 5.26 h−1. The presence of Br− and increase of temperature both accelerated the degradation rate of prometryn during chlorination. The activation energy was calculated as 31.80 kJ/mol. Meanwhile 6 disinfection by-products (DBPs) were detected, namely: chloroform (CF), trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN), dichloroacetone, trichloronitromethane (TCNM), and trichloroacetone. Solution pH significantly affected the formation and distribution of DBPs. CF was the most formed carbonated DBP (C-DBP) with the maximum of 217.9 μg/L at pH 8, and its formation was significantly higher in alkaline conditions. For nitrogenated DBPs (N-DBPs), the yields of DCAN and TCAN were significantly higher in acidic conditions, while the maximum of TCNM achieved in neutral conditions. Because the toxicity of N-DBPs is higher than that of C-DBPs, the pH should be controlled in neutral or slight alkaline conditions during prometryn chlorination to effectively control DBP formation and reduce the related toxicity.

Leaching of indium from an indium-and iron-bearing sphalerite concentrate in sulfuric acid– ferric sulfate solution was examined. The effects of various parameters were studied. Increases in the stirring speed, temperature, ferric ion and sulfuric acid concentrations, and decreases in the particle size, enhanced the indium leaching rate. Scanning electron microscopy/energy-dispersive X-ray spectroscopy and X-ray diffraction analyses of the unreacted and reacted sphalerite concentrate particles showed that elemental sulfur was formed and precipitated at the particle surfaces. The results show that dissolution was controlled by a mixed-control process. In the initial stage, the dissolution kinetics was chemically controlled. When more elemental sulfur was present on the particle surfaces, the dissolution kinetics was controlled by mass transfer though the sulfur layer. The activation energy of the chemically controlled step was 33.9 kJ/mol. The reaction orders with respect to the initial sulfuric acid and ferric ion concentrations were approximately 0.74 and 0.60, respectively.

Zinc ferrite is the principal constituent in zinc neutral-leach residue (NLR) which is commonly treated by hot-acid leaching in electrolytic zinc plants. Reductive leaching of zinc ferrite with sphalerite concentrate as a reducing agent was performed. It was found that leaching of zinc ferrite in the presence of sphalerit concentrate was a viable process that effectively extracted zinc and indium and converted Fe 3+ into Fe 2+ at the same time. Reflux leaching tests by two stages were performed to achieve extractions of 98.1% for zinc and 97.5% for indium, and a Fe 2+ /Fe 3+ molar ratio of 9.6 in leach solution was also obtained. The leaching behaviors of other elements, such as iron, copper and tin were also studied. The results showed that iron and copper were completely leached, whereas tin presented lower extraction values.

Ni–Mo ore is a multi-metal complex and unique mineral resource that exists as a black shale. This ore contains more than 4 wt% Mo and at least 2 wt% Ni. Economic value is associated with deriving products from Ni–Mo ore that contains amorphous colloidal sulfides and that is highly active. Under low-temperature hydrothermal conditions (water at 120 °C or more) and in excess oxygen, amorphous sulfides are oxidized easily to metal-sulfate forms, which leads to nickel and molybdenum dissolution. In this study, the effects of agitation speed, temperature, oxygen partial pressure and particle size on the rate of nickel leaching were investigated. The leaching rate was nearly independent of agitation speed above 400 rpm and increased with a decrease in particle size. A temperature increase to 150 °C contributed significantly to the nickel leaching rate. Oxygen pressure influences nickel leaching, with an oxygen pressure of between 0.5 MPa and 0.7 MPa providing the greatest effect. The pressure-leaching behavior of nickel was fitted to a shrinking-core kinetic model. The mathematical analyses indicates that the dissolution process is chemical-reaction controlled during early dissolution, with an activation energy of 42.68 kJ/mol, and the reaction order with respect to the oxygen partial pressure was 0.79. Up to nearly 70 % nickel was dissolved into solution, and product layers of molybdenum and iron oxide were formed on the surface of the Ni–Mo ore particles, which prevented further nickel dissolution. Thereafter, nickel leaching was controlled by liquid-film diffusion, with an activation energy of 11.01 kJ/mol.

A direct hydrometallurgical route for nickel and molybdenum extraction from a nickel–molybdenum (Ni–Mo) ore using pressure acid leaching was studied. The nickel and molybdenum were extracted by acid leaching under oxygen pressure. Compared with traditional roasting methods, this hydrometallurgical method eliminates SO2 and As2O3 emission (the Ni–Mo ore containing 15%–25% S). Compared with existing alkali leaching recovery of molybdenum process, almost all the nickel and considerable molybdenum were extracted in the acid leaching process. Under oxygen pressure conditions, almost all the nickel and a substantial part of the molybdenum were dissolved into the acid leaching liquor and the other part of the molybdenum was left in the acid leach residue. The acid leach residue was further leached under alkaline (NaOH) conditions. Under optimal experimental conditions, the extraction rates nickel and molybdenum reached 97% and 96%, respectively.

The kinetics of hydrothermal sulfidation of synthetic hemimorphite with elemental sulfur was investigated. The effects of stirring speed (100-600 r/min), temperature (120-220 °C), sulfur dosage (mole ratio of 0.6-1.6), and particle size (48-246 μm) on the hemimorphite conversion rate were studied. The results show that the conversion rate of hemimorphite increases with increasing temperature and decreasing particle size. A stirring speed above 400 r/min and a sulfur dosage above 1 have very little effect on the conversion rate. The kinetics analyses of the experimental data under various conditions indicate that the sulfidation process is controlled by the chemical reaction at the early stage of process with activation energy of 50.23 kJ/mol, and then controlled by diffusion through the product layer with activation energy of 11.12 kJ/mol.

Direct flotation of zinc oxide ore is characterized by poor recovery of only around 50% of zinc. Hydrothermal sulfidation of hemimorphite with elemental sulfur resulted in the formation of stable metal sulfide compounds that would enhance zinc recovery by flotation process. The variables considered in the study were sulfur dosage, temperature, time, stirring speed and particle size. Temperature was the most important factor. The experimental data indicated that under the hydrothermal conditions with sulfur dosage 1.2, temperature 220 °C, time 180 min, agitation speed 500rpm and particle size74-106μm, and 73% hemimorphite conversion fraction was achieved.

Hydrothermal sulfidation of pure cerussite with elemental sulfur has been reported in the present paper. The variables considered in the study were temperature, time, particle size and elemental sulfur fraction in the reacting mixture. Temperature was the most important factor, at temperatures above 180°C, PbS and PbSO4 were the only stable reaction products in the sulfidation of cerussite. The experimental data indicated that under the hydrothermal conditions with a particle size of -74+58 m and sulfur fraction in reacting mixture of 15% at 200°C for 120 min, and 92% of lead sulfidation rate was achieved.

Extraction of vanadium(IV) from sulphate acid solution was studied using organophosphorous-based extractants D2EHPA, EHEHPA and CYANEX 272 in kerosene. The different parameters affecting the extraction of vanadium(IV) under equilibrium conditions were separately investigated to elucidate the stoichiometry of the extracted species. The distribution ratio of vanadium increased with increasing equilibrium pH of the aqueous phase, concentration of the extractants and temperature. D2EHPA was found to be a stronger extractant, having greater pH functionality than EHEHPA and CYANEX 272. Extraction of vanadium(IV) by these organophosphorous-based extractants involved cation exchange mechanism, and the extracted species appear to be VOR2(HR)2 in the low equilibrium pH and VOR2 in the higher equilibrium pH, where HR refers to the three acidic extractants.

A hydrometallurgical process was used for selectively extraction of valuable metals from zinc plant residues. The process includes the following two steps. (1) The zinc plant residue is treated by sulfuric acid atmospheric leaching process with KMnO4 as oxidatant to selectively dissolve zinc while leaving most (above 98 pct) of indium and germandium in the iron residues. (2) The iron residues are treated by acidic atmospheric leaching process with NaClO3 as oxidant to dissolve indium and germanium. The valuable metals of indium and germanium in the second leaching solution can be reclaimed by further treatment. The optimum operating parameters of the first stage and the second stage were established by conditional tests. The experimental data indicated that under the conditions employed the zinc extraction in the first stage was above 95%, and the leaching percentage of indium and germanium in the second stage reached 91.6% and 90.7%, respectively.

Hydrothermal sulfidation of pure white lead with elemental sulfur has been studied in the present paper. The variables considered in the study were temperature, time, particle size and elemental sulfur fraction in the reacting mixture. Temperature and time were the most two important factors, with an increase in temperature and holding time the sulfidation extent of lead improved greatly and the constituent of products changed a lot. At temperatures above 140°C, PbS and PbSO4 were the only stable reaction products in the sulfidation of white lead. The experimental data indicated that under the hydrothermal conditions with a particle size of -58+48 μm and sulfur fraction in reacting mixture of 8% at 140 °C for 90 min, and 86% of lead sulfidation extent was achieved.

The present work is concerned with the kinetic study of pressure leaching of zinc silicate ore in sulfuric acid solutions. The effects of leaching temperature, particle size, sulfuric acid concentration and agitation speed on the zinc extraction were evaluated. The results obtained show that the zinc extraction increases with increasing sulfuric acid concentration and leaching temperature. The leaching kinetics was analyzed by using a shrinking core model with diffusion control given by: 1-2/3x-(1-x)2/3=Kt, which represented well the experimental data. The apparent activation energy was determined to be 44.56kJ/mol at temperatures ranging between 80 and 140°C.

We prepared nanometer-sized nickel oxide by hydrothermal decomposition. In this work, NiSO4•6H2O and Na2CO3 were used as raw materials to prepare the precursors. Nanometer-sized nickel oxide was obtained after calcining the precursors. The temperature of the calcination process affects the morphology and size of the nanometer-sized nickel oxide. The precursors and products were analyzed by TG, XRD and SEM. Sheet nanometer-sized nickel oxide was obtained and characterized by its high purity, smooth surface, regular hexagon shape, average size of 500 nm and 30-60 nm thickness. The results indicate that the NiO particles become open pore structures at a calcination temperature above 500 °C

In the present work, contamination and potential ecological risk of six heavy metals (Pb, Cd, Hg, As, Cu and Zn) in sediments of Aha Lake, one of the five drinking water sources for Guiyang City, were assessed based on a method which is associated with toxic-response factors of contaminants. For comparison, the two sets of reference data representing the pre-industrial and the local baseline pollution levels were employed. When the pre-industrial levels were taken as references, the accumulating coefficients on average diminished in the order of Zn > As > Hg > Cd > Cu > Pb, and the potential ecological risk descended in the order of Hg > Cd > As > Cu > Zn > Pb. When the local baseline values worked as references, the accumulating coefficients on average diminished in the order of Cd > Zn > Hg > Cu > As > Pb, and the potential ecological risk descended in the order of Cd > Hg > As > Cu > Zn > Pb. It is evident that Cd and Hg are the critical elements in terms of potential ecological hazard in Aha Lake among these six heavy metals.

Leaching behaviors of zinc, copper, indium and iron from a sphalerite concentrate in sulfuric acid-oxygen system has been investigated in the present paper. Various parameters were studied including particle size, concentration of sulfuric acid, partial pressure of oxygen, leaching temperature, and leaching time. The experimental data indicated that under the typical plant conditions employed up to 99% zinc , 85% copper and 90% indium extraction were achieved. The mineralogical analysis of the residue showed that the main minerals are elemental sulphur, unreacted pyrite and quartz, the amount of sulphide sulphur oxidized to sulfur during leaching is 81%. This process provides an effective way for the extraction of zinc, copper and indium from sphalerite concentrate.

This paper reports a study on distribution characteristics of phosphorus and its species in 20 sediments samples from Lakes Baihua and Aha, based on the technique of sequential extraction. Baihua and Aha, two man-made reservoirs, are key drinking-water sources. The results, compatible with local geophysical characteristics, indicate that in sediments from both lakes, the concentrations of inorganic phosphorus (IP) were higher than those of organic phosphorus (OP), and the IP consisted mainly of calcium-bound phosphorus (Ca-P), which may temporarily control phosphorus release. Moreover, the concentrations of total phosphorus (TP) in both lakes sediments were high, thus phosphorus release potential and bioavailability were highly significant. Further statistical analyses revealed significant correlations with two extractable principal components allowing interpretation of possible origins of phosphorus loadings. Furthermore, available remediation measures were briefly evaluated for both lakes in consideration of their distinctive environmental features.

The recovery of vanadium from a black shale from Guizhou Province of China was performed using a three-step process, which consists of a leaching step in the H2SO4-HF-NaClO system under atmospheric pressure, the vanadium separation from leachate by solvent extraction and stripping, followed by precipitation of ammonium vanadate and thermal decomposition. Under the optimum leaching conditions of 100 g/L sulfuric, 15 g/L hydrofluoric acid, 1.5 g/L NaClO, 6 h leaching at 90 °C and oxygen partial pressure of 1 200 kPa, and the liquid-to-solid ratio of 2, about 91% vanadium extraction is achieved. The vanadium extraction yields of solvent and stripping are 99.83% and 97.66% when using 10% (volume fraction) P204, 5% TBP and 85% sulfonated berosene as organic phase and 15% (mass fraction) sulphuric acid as stripping agent. After thermal decomposition the purity of powder vanadium pentoxide products is 99.18% and the overall vanadium recovery is over 81% in the whole process.

Zinc silicate ore was characterized mineralogically and the results showed that zinc exists mainly as hemimorphite and smithsonite in the sample. Sulfuric acid pressure leaching of zinc silicate ore was carried out to assess the effect of particle size, sulfuric acid concentration, pressure, reaction time and temperature on the extraction of zinc and the dissolution of silica. Under the optimum conditions employed, up to 99.25% of zinc extraction and 0.20% silica dissolution are obtained. The main minerals in leaching residue are quartz and small amounts of undissolved oxide minerals of iron, lead and aluminum are associated with quartz.

Vanadium extraction from stone-coal was investigated by oxygen pressure acid leaching and solvent extraction. The mineralogy of the stone-coal from Tongren City of Guizhou Province, China, was investigated by various determination methods. The effects of leaching time, leaching temperature, leaching agent concentration, leaching L/S ratio, granularity of material, additive consumption were investigated based on the mineralogy. The results show that under the conditions of leaching time of 3–4 h, temperature of 150 °C, sulfuric acid consumption of 25%–30%, ratio of liquid to solid of 1.2:1, the granularity less than 0.074 mm, additive consumption of 3%–5%, and oxygen pressure of 1.2 MPa, and the vanadium leaching rate can be more than 92% by the method of two-step pressurized acid leaching. The powdery V2O5 product with 99.52% in V2O5 content is obtained by the flowsheet of acid recovery, removing iron by reduction process, solvent extraction, precipitating vanadium with ammonium water, and pyrolysis from the stone-coal oxygen pressure acid-leaching solution. The total recovery efficiency of vanadium is above 85%, which is more than 20% higher than that obtained in the conventional process. Furthermore, the new process does not cause air pollution since no HCl or Cl2 is released by calcination of the raw material.

Extraction of vanadium from black shale was attempted in pressure acid leaching. The chemical components of the sample obtained from Guizhou Province of China show that it contains 3.258% V 2 O 5 , 52.880% SiO 2 and 16.140% Al 2 O 3 . Phase analyses of vanadium indicates vanadium mainly exists in the free oxide and mica. Vanadium contents in the two phases are 18% and 53%, respectively. The contents of V 3+ , V 4+ and V 5+ are almost equal. Under the optimum parameters of one-step leaching (reaction time of 3 h, sulfuric addition of 25%, temperature of 150 °C, liquid to solid ratio of 1.2 mL/g, catalyst (FeSO 4 ) addition of 5% and size of 85% particle 0.074 mm), about 77% of vanadium is recovered. After two-step countercurrent leaching, the leach recovery of vanadium can reach above 90%. Air replacing oxygen is completely feasible. The impurity metals can dissolve into solution in different degrees.