Precipitation Of Zinc Sulfide Research Articles

Polyvinyl alcohol stabilized ZnS nanoaggregates using organosulfur source for photocatalytic disintegration of methyl orange dye

ZnS nanoaggregates surface-passivated by a hydroxyl-based polymer matrix, polyvinyl alcohol (PVA), have been synthesized using a wet chemical method and an organosulphur precursor. The nanocomposite was characterized by XRD, SEM, and FTIR. XRD patterns revealed wurtzite structure. FTIR spectrum confirmed the interaction of hydroxyl group of PVA with the ZnS. We proposed a probable pathway for the precipitation of zinc sulfide by alkaline hydrolysis of complex formed from (NH2)2CS and Zn2+-polymer complex. The optical properties were monitored using UV–Vis spectroscopy and photoluminescence (PL) spectroscopy. Quantum confinement of electrons is confirmed by increase in the optical band gap and determined to be 3.91 eV. The photocatalytic activity of the ZnS/PVA nanoaggregates particles was examined using methyl orange (MO). After 3 h of illumination, the photocatalytic degradation rate of methyl orange (MO) is about 94.20 %.

Study of Copper and Zinc Extraction from Underspoil Water

The subject of study was the Safyanovskaya Med company’s acidic underspoil water containing 0.17 g/liter of copper and 1.8 g/liter of zinc (pH 2.8–2.9). The goal was to study and develop a technology of cleaning water of impurities (copper, zinc, aluminum, iron, manganese), accompanied by extraction of copper and zinc in the form of commercial products. Copper extraction by cementation with metallic iron was studied. It was shown that this method could allow extracting 94–95% copper into a concentrate. The role of resolution processes of precipitated copper in cementation was established. To reduce the consumption of iron and to improve the quality of precipitated copper, it is proposed to carry out cementation in a washbox. The copper content in the concentrate was 27–28%, while the specific consumption of iron was 7.0–7.5 kg/kg of copper. During the studies of material composition of copper precipitate, the formation of cuprospinel, goethite, and bassanite phases and the precipitation of basic aluminum sulfates were detected. The extraction of zinc from the solution after copper removal was studied by precipitation with sodium sulfide. As a result, a concentrate was obtained with a zinc content of 49.6–50.9% with extraction of 99%. The process regularities for zinc concentrate dehydration were studied. By optimizing the crystallization conditions of the precipitate, a minimum final cake moisture content of 40–42% was reached. A process flow diagram for acidic underspoil water, including copper cementation and the precipitation of zinc sulfide, was developed. According to this diagram, the mother solution from zinc precipitation should be treated with lime until the pH reaches 10–10.5, followed by slurry settling. As a result, clean water of the following composition is obtained, mg/liter: 0.05 zinc, 0.01 copper, 0.02 aluminum, < 0.02 iron, 0.05 manganese. These values correspond to the quality of drinking water according to GOST R 51232-98.

Visual MINTEQ model, ToF–SIMS, and XPS study of smithsonite surface sulfidation behavior: Zinc sulfide precipitation adsorption

Abstract In this study, we investigate the smithsonite surface sulfidation by zinc sulfide precipitation adsorption. Smithsonite solubility experiments indicated that the CZnT in Na2S solution (1.0 × 10−3 mol/L) was 1–2 orders of magnitude lower compared with the corresponding experiment results in deionized water. Na2S addition benefited the dissolution rate of smithsonite in deionized water. Visual MINTEQ model results confirmed that the zinc sulfide precipitation formed after the main sulfidation reaction between Zn(OH)2(aq) and HS− ions at pH 10, compared with the conversion from ZnS(aq), Zn2S32− ions, and Zn4S64− ions to sphalerite. Moreover, X-ray diffraction and X-ray photo-electron spectroscopy (XPS) analysis showed that the average crystallite sizes of zinc sulfide precipitation particle obtained by co-precipitation technique were approximately 2.32 nm in size. These particles were composed of zinc monosulfide and zinc polysulfide. Time-of-flight secondary ion mass spectrometry and XPS analysis provided strong evidence for zinc sulfide precipitation adsorption on the smithsonite surfaces. Furthermore, more mass signals of S−, ZnS−, S2−, and Zn2S− were observed from the zinc sulfide precipitation than from natural sphalerite, and the monosulfide in the zinc sulfide precipitation was easily adsorbed on the smithsonite surfaces. Results elucidate the smithsonite surface sulfidation behavior during zinc sulfide precipitation adsorption.

Spatial impacts of inorganic ligand availability and localized microbial community structure on mitigation of zinc laden mine water in sulfate-reducing bioreactors

Sulfate-reducing bioreactors (SRBRs) represent a passive, sustainable, and long-term option for mitigating mining influenced water (MIW) during release. Here we investigate spatial zinc precipitation profiles as influenced by substrate differentiation, inorganic ligand availability (inorganic carbon and sulfide), and microbial community structure in pilot-scale SRBR columns fed with sulfate and zinc-rich MIW. Through a combination of aqueous sampling, geochemical digests, electron microscopy and energy-dispersive x-ray spectroscopy, we were able to delineate zones of enhanced zinc removal, identify precipitates of varying stability, and discern the temporal and spatial evolution of zinc, sulfur, and calcium associations. These geochemical insights revealed spatially variable immobilization regimes between SRBR columns that could be further contrasted as a function of labile (alfalfa-dominated) versus recalcitrant (woodchip-dominated) solid-phase substrate content. Both column subsets exhibited initial zinc removal as carbonates; however precipitation in association with labile substrates was more pronounced and dominated by metal-sulfide formation in the upper portions of the down flow columns with micrographs visually suggestive of sphalerite (ZnS). In contrast, a more diffuse and lower mass of zinc precipitation in the presence of gypsum-like precipitates occurred within the more recalcitrant column systems. While removal and sulfide-associated precipitation were spatially variable, whole bacterial community structure (ANOSIM) and diversity estimates were comparatively homogeneous. However, two phyla exhibited a potentially selective relationship with a significant positive correlation between the ratio of Firmicutes to Bacteroidetes and sulfide-bound zinc. Collectively these biogeochemical insights indicate that depths of maximal zinc sulfide precipitation are temporally dynamic, influenced by substrate composition and broaden our understanding of bio-immobilized zinc species, microbial interactions and potential operational and monitoring tools in these types of passive bioreactors.

Influence of Soil Properties on Zinc Solubility Dynamics Under Different Redox Conditions in Non–Calcareous Soils

Zinc (Zn) deficiency in paddy soils is often a problem for rice production. Flooding can decrease metal availability in some non–calcareous soils through different mechanisms associated with soil redox status. Laboratory experiments were performed in order to better understand the processes that governed the dynamics of Zn in non–calcareous paddy soils at varying redox potentials (Eh). Air–dried non–calcareous soil samples collected from four different paddy field sites in the Philippines were submerged and incubated in a reaction cell with continuous stirring and nitrogen purging for 4 weeks, and then purged with compressed air for another week to reoxidize the system. The Eh of the four soils started at 120 to 300 mV, decreased to −220 to −300 mV after 100 to 250 h of reduction, and was maintained at this low plateau for about 2 weeks before increasing again upon reoxidation. Zinc solubility showed contrasting patterns in the four soils, with two of the soils showing a decrease in soluble Zn as the Eh became low, probably due to zinc sulfide (ZnS) precipitation. In contrast, the other two soils showed that Zn solubility was maintained during the reduced phase which could be due to the competition with iron (Fe) for precipitation with sulfide. Differences in the relative amounts of S, Fe, and manganese (Mn) oxides in the four soils apparently influenced the pattern of Zn solubility after flooding.

Effect of post-precipitation conditions on surface properties of colloidal metal sulphide precipitates

Metal sulphide precipitation is important in several hydrometallurgical processes. However, challenges exist in solid–liquid separation and recovery of the colloidal precipitates produced in some systems. This study presents the effect of downstream processing options on the surface properties of colloidal particles produced during copper and zinc sulphide precipitation. XRD and EDAX characterisation indicated the copper precipitate was a mixture of covellite (63%) and copper hydroxysulphate (37%), while the zinc sulphide was more pure, but less crystalline. The effect on surface charge and aggregation tendency of different concentrations of background electrolyte (1–100mM KCl), suspension pH, aqueous sulphide, a divalent (Ca2+) and trivalent (Al3+) cation were studied. The magnitude of the negative surface charge increased with increasing suspension pH (pH 6 to pH 11) for both copper and zinc precipitates. The addition of aqueous sulphide (0.84mM) to the zinc precipitate resulted in a significant decrease in the zeta potential and suppressed aggregation, due to adsorption of the negatively charged sulphide ions. This effect was reduced at high ionic strength. A higher sulphide concentration was required to replicate the phenomenon with the copper precipitate due to sulphidisation of the copper hydroxysulphate initially. Addition of a divalent cation (Ca2+) to the suspension had little effect on the surface charge of the particles and did not promote aggregation. However, addition of a small amount (0.5mM) of Al3+ ions resulted in a significant change in surface charge (−30 to −10mV for copper and −23mV to −5mV for zinc) and subsequent aggregation. The results of this study show that downstream processing of colloidal metal sulphide precipitates, produced where supersaturation cannot be managed, can lead to effective solid–liquid separation, by changing the surface properties of the precipitate.

Metal sulphides from wastewater: Assessing the impact of supersaturation control strategies

Metal sulphide precipitation forms an important component of acid mine drainage remediation systems based on bacterial sulphate reduction. However, the precipitation reaction is inherently driven by very high levels of supersaturation with the generation of small particles with poor solid–liquid separation characteristics. In this study, the effect of strategies used to manage supersaturation was investigated during copper and zinc sulphide precipitation reactions. Initial batch studies showed the origin of sulphide (biological or chemical) had no significant effect on the efficiency of zinc sulphide precipitation. For copper, low metal removal efficiency was obtained at metal to sulphide molar ratios below 1.6 in the synthetic sulphide system. This was improved in the biogenic sulphide system, due to the presence of residual volatile fatty acids, but the presence or absence of particulate organic matter had no effect on recovery. Subsequent studies, conducted using synthetic sulphide solutions in a seeded fluidised bed reactor with multiple reagent feed points (2FP and 6FP) and different recirculation flow rates (300 and 120 mL min−1) showed efficient zinc sulphide precipitation, but limited (<10%) deposition on the seeds. Increasing the number of sulphide feed points (2–6) reduced precipitate loss as fines by approximately 10%. Zinc sulphide fines could be effectively recovered from suspension by settling under quiescent conditions. In the copper system, metal recovery was low (ca 40%) due to the formation of very small copper sulphide particles (mean particle size of ca 0.01 μm). Increasing the number of reagent feed points did not affect supersaturation to the extent of altering particle characteristics. The copper sulphide fines could not be recovered by settling, remaining in a stable colloidal suspension due to their highly charged surfaces (zeta potential −50 mV). The change in recirculation flow rate had a limited effect (ca 5% improvement) on process efficiency. The results show that the extremely high supersaturation prevalent during metal sulphide precipitation is difficult to control using conventional approaches and suggest that the seeded fluidised bed reactor is not suitable for this application.

Measuring free tissue sulfide

Hydrogen sulfide is synthesized endogenously in mammals and has been shown to have both physiological and pathological functions. So far there has been little agreement as to the actual levels of endogenous sulfide under physiological or pathological conditions; this is partly due to the complexity involved in measuring free sulfides due to H2S volatility, oxidation, reactivity and the presence of bound labile sulfur in tissues. In this report we describe a method of measuring free tissue sulfides using a zinc sulfide precipitation and wash method. It is an indirect method that measures the sulfide difference between samples prepared at pH 9 and pH 6, assuming that at pH 9 free sulfides would be retained in solution, while at pH 6 free sulfides would volatilize during sample preparation. Using this approach we were able to measure appreciable amounts of free sulfides in mouse: lung, pancreas, liver and kidney at 0.036 + 0.006, 0.082 + 0.009, 0.215 + 0.016 and 0.323 + 0.031 nmole per mg of tissue respectively (n = 6).

Selective removal of transition metals from acidic mine waters by novel consortia of acidophilic sulfidogenic bacteria

SummaryTwo continuous‐flow bench‐scale bioreactor systems populated by mixed communities of acidophilic sulfate‐reducing bacteria were constructed and tested for their abilities to promote the selective precipitation of transition metals (as sulfides) present in synthetic mine waters, using glycerol as electron donor. The objective with the first system (selective precipitation of copper from acidic mine water containing a variety of soluble metals) was achieved by maintaining a bioreactor pH of ∼2.2–2.5. The second system was fed with acidic (pH 2.5) synthetic mine water containing 3 mM of both zinc and ferrous iron, and varying concentrations (0.5–30 mM) of aluminium. Selective precipitation of zinc sulfide was possible by operating the bioreactor at pH 4.0 and supplementing the synthetic mine water with 4 mM glycerol. Analysis of the microbial populations in the bioreactors showed that they changed with varying operational parameters, and novel acidophilic bacteria (including one sulfidogen) were isolated from the bioreactors. The acidophilic sulfidogenic bioreactors provided ‘proof of principle’ that segregation of metals present in mine waters is possible using simple online systems within which controlled pH conditions are maintained. The modular units are versatile and robust, and involve minimum engineering complexity.

Pilot scale investigation of zinc and sulphate removal from industrial discharges by biological sulphate reduction with molasses as electron donor

A biological sulphate reduction process, with molasses as an electron donor, was used for the removal of zinc and sulphate from Rayon industrial wastewater. The process involved reduction of sulphate to sulphide under anaerobic conditions. The sulphide‐rich effluent was used to remove zinc as zinc sulphide precipitate. The investigation was conducted at pilot scale with real wastewater from the Rayon industry as feed. The effects of sulphate loading rate and temperature of feeding wastewater were evaluated. The experimental results showed that there was no significant difference in sulphide production when the reactor was operated at 50 ± 2 °C and 65 ± 2 °C. Sulphide production was in the range of 500–515 mg L−1. In addition, an increase in sulphate loading rate from 6.3 ± 0.7 kg SO4 m−3 d−1 to 14.9 ± 2.4 kg SO4 m−3 d−1 resulted in a dramatic decrease in sulphate removal efficiency. Furthermore, zinc sulphide precipitation at pH 7 removed more than 96% of zinc.

Precipitation dynamics of zinc sulfide multiscale agglomerates

AbstractHomogeneous precipitation of zinc sulfide from thioacetamide decomposition in presence of zinc sulfate in acid solution results in the formation of four‐scale agglomerates. We present here experimental results relative to the monitoring of several physicochemical (pH, electrical conductivity, concentration in sulfide ions, turbidity) and morphological (agglomerate shape and size) parameters throughout the precipitation process. From these parameters essential characteristics of the precipitation process can be determined, especially the supersaturation level and the precipitated product mass. From this information and with the help of microphotographs of samples withdrawn at different stages of the precipitation, it is possible to formulate a new mechanism of zinc sulfide precipitation. In particular, the nature of the different agglomeration scales is elucidated as well their succession in time. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Modelling and on-line estimation of zinc sulphide precipitation in a continuously stirred tank reactor

In this paper the ZnS precipitation in a continuously stirred tank reactor (CSTR) is modelled using mass balances. The dynamics analysis of the model reveals that the ZnS precipitation shows a two time-scales behaviour with inherent numerical stability problems, which therefore needs special attention during implementation. The mass balance model allows the design of an on-line estimator of the zinc concentration and precipitation rate, given only wet-chemical measurements of the sulphide concentration and of the pH in the reactor. The on-line estimation algorithm, also called observer or software sensor, is tested in a simulation experiment with a block disturbance showing numerically stable results. Furthermore, on the basis of real-world experimental data, the observer shows an appropriate performance. The estimation procedure offers good possibilities to be applied for other metal removal processes.

On-line estimation of the dissolved zinc concentration during ZnS precipitation in a continuous stirred tank reactor (CSTR)

In this paper a method is presented to estimate the reaction term of zinc sulphide precipitation and the zinc concentration in a CSTR, using the read-out signal of a sulphide selective electrode. The reaction between zinc and sulphide is described by a non-linear model and therefore classical observer theory cannot be applied directly, as this theory was initially developed for linear systems. However, by linear reparametrization of this non-linear system, the linear observer theory can be applied in an effective way. This is illustrated by a zinc sulphide example using real data.

Treating Industrial Discharges by Thermophilic Sulfate Reduction Process with Molasses as Electron Donor

Thermophilic sulfate reduction process with molasses as an electron donor was investigated for the removal of zinc from rayon industry wastewater. Sulfide rich effluent from the process was used to remove zinc as zinc sulfide precipitate. The investigations with sulfate reduction process were conducted with synthetic (Stage I) as well as real wastewater from Rayon industry (Stage II) as feed. The effect of feed COD: sulfate ratio, which is the key factor for operating the sulfate reduction process, was focused on in this study. The experimental results showed that the process could achieve a high sulfate conversion rate of about 7.22 ± 1.91 g SO4 l−1.d−1 at COD: sulfate ratio of 1.5:1 and 7.20 ± 2.27 g SO4 l−1.d−1 at COD: sulfate ratio of 3:1 during stage I and stage II, respectively. At the end of the operation of stage II, a maximum sulfide production of 496.2 mg S l−1 was achieved at COD: sulfate ratio of 3:1. Furthermore, sulfide rich effluent from sulfate reduction process was used for zinc sulfide precipitation. The results showed that more than 95% of zinc was removed from a high sulfate-containing wastewater.

Seasonal influence on sulfate reduction and zinc sequestration in subsurface treatment wetlands

To characterize the effects of season, temperature, plant species, and chemical oxygen demand (COD) loading on sulfate reduction and metals removal in treatment wetlands we measured pore water redox potentials and concentrations of sulfate, sulfide, zinc and COD in subsurface wetland microcosms. Two batch incubations of 20 day duration were conducted in each of four seasons defined by temperature and daylight duration. Four treatments were compared: unplanted controls, Typha latifolia (broadleaf cattail), and Schoenoplectus acutus (hardstem bulrush), all at low COD loading (267 mg/L), plus bulrush at high COD loading (534 mg/L). Initial SO 4-S and zinc concentrations were 67 and 24 mg/L, respectively. For all treatments, sulfate removal was least in winter (4 °C, plant dormancy) greatest in summer (24 °C, active plant growth) and intermediate in spring and fall (14 °C), but seasonal variation was greater in cattail, and especially, bulrush treatments. Redox measurements indicated that, in winter, plant-mediated oxygen transfer inhibited activity of sulfate reducing bacteria, exacerbating the reduction in sulfate removal due to temperature. Doubling the COD load in bulrush treatments increased sulfate removal by only 20–30% when averaged over all seasons and did not alter the basic pattern of seasonal variation, despite tempering the wintertime increase in redox potential. Seasonal and treatment effects on zinc removal were broadly consistent with sulfate removal and presumably reflected zinc-sulfide precipitation. Results strongly suggest that interactive effects of COD loading rate, temperature, season, and plant species control not only sulfate reduction and zinc sequestration, but also the balance of competition between various microbial consortia responsible for water treatment in constructed wetlands.

Dynamic Modelling and Process Control of ZnS Precipitation

This paper presents the dynamic modelling and design of a control strategy for the ZnS precipitation process. During lab‐scale experiments, the sulfide concentration in a precipitator was controlled at a prespecified pS value by manipulating the flow from a buffer vessel. Batch tests showed that the optimal condition for zinc sulfide precipitation is at a sulfide concentration of 10−15 mole/l (pS 15). Experiments with the precipitator showed that the sulfide concentration highly deviates from a given setpoint when proportional (P) control is used, but this deviation can be decreased using a Proportional Integral (PI) controller. Moreover, the PI controller was able to handle sudden disturbances in the process conditions (pH, influent flow rate, or zinc and sulfide concentration). Additional precipitation experiments were conducted using effluent from a sulfate reducing gas‐lift reactor to determine if the compounds present in the effluent influence the control process. With the gas‐lift reactor effluent and a PI controller, the desired sulfide concentration was reached almost instantaneously (within 15 minutes) within acceptable margins (2–5%).

Use of biogenic sulfide for ZnS precipitation

A 600 ml continuously stirred tank reactor was used to assess the performance of a zinc sulfide precipitation process using a biogenic sulfide solution (the effluent of a sulfate-reducing bioreactor) as sulfide source. In all experiments, a proportional-integral (PI) control algorithm was used to control the pH and the sulfide (S 2−) concentration at the desired level in the precipitator. The pS (defined as: −log [S 2−]) and pH were optimised using a chemical Na 2S solution as sulfide source. A S 2− concentration of 10 −15 M (i.e. pS 15) was found to be optimal for zinc sulfide precipitation, resulting in a residual zinc concentration of 0.07 mg/l from a 3 g/l Zn 2+ influent, for both chemical Na 2S and biogenic sulfide solutions. The mean particle size of the ZnS precipitates at pS 15 and pH 6.3 was 7.5 and 10.2 μm when using biogenic sulfide and chemical Na 2S, respectively, indicating that both sulfide sources are adequate for solid–liquid separation by sedimentation. When biogenic sulfide instead of chemical Na 2S was used, the efficiency of the ZnS precipitation process slightly decreased both in terms of zinc effluent concentration (at pS 10 and 20) and particle size of the precipitate (at pS 10, 15 and 20). This was shown to be attributed to the presence of various substances (phosphate, micro-nutrients, acetate, EDTA) present in the sulfate-reducing reactor effluent.

Occurrence of methanogenesis during start-up of a full-scale synthesis gas-fed reactor treating sulfate and metal-rich wastewater

The start-up of a full-scale synthesis gas-fed gas-lift reactor treating metal and sulfate-rich wastewater was investigated. Sludge from a pilot-scale reactor was used to seed the full-scale reactor. The main difference in design between the pilot- and full-scale reactor was that metal precipitation and sulfate reduction occurred in the same reactor. After 7 weeks the full-scale reactor achieved the sulfate conversion design rate of 15 kg/m 3 day. Zinc sulfide precipitation inside the reactor did not interfere with obtaining a high rate of sulfate reduction. 16S rRNA gene analysis demonstrated that the bacterial communities in both reactors were dominated by the sulfate-reducing genus Desulfomicrobium. Archaeal communities of both reactors were dominated by the methanogenic genus Methanobacterium. Most Probable Number (MPN) counts confirmed that heterotrophic Sulfate-Reducing Bacteria (SRB) were dominant (10 11–10 12 cells/g VSS) compared to homoacetogens (10 5–10 6 cells/g VSS) and methanogens (10 8–10 9 cells/g VSS). Methanogenesis was not suppressed during start-up of the full scale-reactor, despite the predominance of SRB, which have a lower hydrogen threshold. Due to the short sludge retention time (4–7 days) competition for hydrogen is determined by Monod kinetics, not hydrogen thresholds. As the kinetic parameters for SRB and methanogens are similar, methanogenesis may persist which results in a loss of hydrogen.

硫化水素を用いたＣｕ，Ｚｎ，Ｎｉ混合めっき廃水の選択的硫化による金属硫化物の分離

Experiments were conducted to investigate selective sulfuration of copper, zinc and nickel contained in a simulated plating wastewater using H2S as a sulfurating agent. The sulfuration of single solutions of copper, zinc and nickel, and mixed solutions of these metals with H2S was conducted in a bubble column reactor.As a result, it was found that heavy metals can be selectively precipitated from the mixed-metal plating wastewater at a pH value of 1.5 for copper, 4.5 for zinc and 6.7±0.2 for nickel. The purities of precipitates based on total amount of metal contained were 95.5%, 87.4% and 94.7% in the case of copper, zinc and nickel, respectively. When the results were compared with those obtained for the selective precipitation with Na2S, it was found that higher purities of metal sulfides were achieved with H2S. It was considered that local increases of pH resulting from an addition of alkaline sulfurating agent of Na2S were avoided in the case of H2S. Consequently, an undesirable co-precipitation of zinc and nickel sulfides at a pH value of 1.5 corresponding to copper selective precipitation was reduced. Similarly, the precipitation of nickel sulfide was partially avoided during the precipitation of zinc sulfide at a pH value of 4.5.

49.1: Improved Zinc‐Sulfide‐Type Phosphors by a Novel Synthetic Method

AbstractA novel, quick, and “clean”, method has been developed for the preparation of zinc sulfide phosphors for CRT and FED applications. The method involves the addition of a solution of sulfur in hydrazine monohydrate to a zinc salt solution, which results in precipitation of zinc sulfide, Firing this material has resulted in bright, efficient phosphors with improved luminescent properties between 500–15,000 eV, particularly for copper and silver activated ZnS.