Zinc Precipitation Research Articles

Mechanism and kinetics of ultrasound-enhanced CaCO3 precipitation for indium enrichment in zinc oxide dust leaching solution

In this study, ultrasound-enhanced calcium carbonate precipitation was used to enrich indium in zinc oxide dust leachate, and the effects of precipitation endpoint pH and ultrasound power on the indium precipitation behaviour were investigated, and the optimal conditions of ultrasound-enhanced precipitation were obtained to be the precipitation endpoint pH of 4.0 and the ultrasound power of 200 W. The precipitation rate of indium under these conditions was 99.79 %. At the same time, the effects of ultrasonication and conventional stirring on the indium precipitation kinetics were compared, which proved that ultrasound can shorten the time for precipitation to reach equilibrium and reduce the amount of calcium carbonate used, and the theory of ultrasonication activation energy was put forward. The activation energy of ultrasonication was Eu-a = 2.63 KJ/mol, and that of conventional precipitation was 9.78KJ/mol, which proved that ultrasonication could reduce the activation energy of the precipitation reaction, and promote the rapid precipitation reaction. The kinetic model of ultrasound-enhanced indium precipitation is lnC0-lnCt = exp(0.11339–318.54/W).t + A. In addition, the mechanism of ultrasound-enhanced calcium carbonate precipitation of indium was revealed by XRD, SEM-EDS, XPS and TEM analyses of the precipitated residue, it was demonstrated that ultrasound can inhibit the precipitation of zinc, and the ZnCO3 phase was found in the ultrasonically precipitated residue. This study provides a new idea for indium enrichment, and the future focus will be on the scale-up of the ultrasound-enhanced precipitation device.

Cost-effective microbial induced ZnO synthesis for building material: Antibacterial, photocatalytic and mechanical characteristics

Utilization of effective and economical nanoparticles/nanocomposite materials in civil engineering is still remaining a significant challenge in current research arena. In this study, microbial-induced precipitation was formulated for integration of white cement mortar to enhance efficiency and evaluate its potential applications in antibacterial and photocatalytic degradation of methylene blue. Hexagonal wurtzite structure of synthesized ZnO exhibited high crystallinity with significant contribution of hydration product after 28days analysis. Morphology of produced material showed less homogeneity with high densification and morphology altered from needles-like structure to tube with the integration of adsorbent ratio from ZnO-0 to 2.5, presented all the required chemical components in EDXS analysis. The water absorption rate in sample slurry of ZnO-2.5 exhibited significant reduction of 52.75 % compared to baseline water absorption rate of 12.71 % in commercial ZnO and contact angle was noted higher as 89.54°, which indicates hydrophilic character of material. The highest compressive strength of sample ZnO-2.5 was noted 508.89 kgf/cm2 in 28days of wet curing method, indicated the effective gel formation of calcium silicate in samples. Maximum methylene blue dye degradation recorded 79.95 % in case of using ZnO-2.5, which showed another influential character with excellent efficiency. In addition, prepared sample has shown almost complete bactericidal efficiency under simulated sunlight. Compared to commercial white cement mortar, biological white cement mortar can save NT$149,531 per cubic meter at industrial scale. Therefore, results indicate that microbial-induced zinc precipitation incorporated using hydrothermal preparation of biological white cement mortar improves the surface properties for applications and reduces its cost of study.

TSQ Incubation Enhances Autometallographic Zinc Detection in Cultured Astrocytes.

Zinc is a critical ion for a large number of cellular functions. In the central nervous system, zinc ions are involved in synaptic transmission. Therefore, zinc homeostasis is essential, and cells have developed a variety of mechanisms to control cellular zinc concentration, including the zincosome formation. Alterations of free zinc levels have been associated with brain dysfunction and are present in many illnesses and syndromes. Astrocytes are implicated in the maintenance of the neuronal milleu and brain homeostasis. In this work, we have analyzed the combination of direct (TSQ) and indirect (autometallography) zinc detection methods to increase sensitivity for studying zinc uptake by rat astrocytes in vitro. Zincosome formation was visualized with the zinc fluorochrome TSQ by light microscopy. Additionally, we improved both zinc precipitation and cellular fixation methods to preserve zinc ions and make them suitable for autometallography development. Our tests pinpointed paraformaldehyde and sodium sulfide as the more adequate methods for cellular fixation and zinc precipitation, respectively. TSQ incubation and pH of the fixative were shown to be crucial for autometallography. Using this improved method, we visualized the zinc content of zincosomes at the ultrastructural level both as silver autometallographic precipitates and as electrodense sulfide-osmium zinc precipitates.

Formation of zinc carbonate phases on dissolving calcite, aragonite, and vaterite in acidic aqueous solutions

Calcium carbonate (CaCO3) minerals serve as a major sink to retain metal ions through mineral-water interfacial reactions in which the capacity and long-term stability of contaminant uptake are influenced by coupled dissolution and precipitation reactions of both primary and secondary carbonate minerals (i.e., mineral replacement). Notably, recent studies of calcite reactivity in acidic solutions containing high levels of metal ions demonstrated complex behavior under conditions of sustained disequilibrium. We explored the reactivity of three CaCO3 polymorphs (calcite, aragonite, and vaterite) with acidic Zn2+-containing aqueous solutions using a suite of imaging techniques including optical and scanning electron microscopies, synchrotron-based micro X-ray fluorescence, and transmission X-ray microscopy. Zn uptake by calcite occurred through a two-step process: the formation of a thin layer of the zinc precipitate on the substrate surface followed by the growth of fibrous and radiating hydrozincite particles from the layer. In contrast, Zn uptake by aragonite occurred by mineral replacement where the secondary Zn carbonate phase preserved the external morphology of the original crystal (i.e., a pseudomorph). The replacement of vaterite by hydrozincite occurred within the confined space beneath the porous shell of vaterite, signifying that the primary mechanism driving Zn carbonate precipitation was chemical exchange through the pores. When multiple CaCO3 polymorphs coexisted, the replacement of aragonite and vaterite occurred preferentially over that of calcite. These results demonstrate the distinct morphological and mineralogical controls over the reactivities of calcium carbonate minerals with Zn2+ under acidic conditions.

Gold recovery from roasted refractory gold concentrate through cyclic extraction using MnO2-assisted thiocyanate leaching and cementation with zinc powder

Cyanidation has long served as the industrial standard in the gold industry, necessitating heightened attention to cyanide management owing to its inherent toxicity. This study developed a novel MnO2-assisted thiocyanate leaching system as an alternative to cyanide. The sample was generated from a refractory gold concentrate processed by roasting, containing 54.4 g/t gold with iron oxide and quartz as the major mineral phases. Within the framework of the novel system, gold recovery was investigated in terms of gold association, recovery behavior, thermodynamics, and optimization using cyclic extraction protocols. The most suitable leaching conditions were determined as 1.20 mol/L NaSCN, 4.00 mmol/L MnO2, pH at 1.00, liquid-to-solid ratio of 4 mL/g, and leaching duration of 24 h, resulting in a maximum gold extraction of 94.8%. Subsequent zinc precipitation facilitated a gold recovery of 99.4% from the leachate. Furthermore, the implementation of a cyclic extraction scheme, coupled with reagent addition to offset consumption, yielded a significant thiocyanate dosage reduction by 75% while maintaining gold recovery. This acidic leaching system yields satisfactory gold recovery with minimized reagent consumption, particularly suited for refractory gold ore that has undergone acidic pretreatment.

Closed-loop process for Zn and Cu selective recovery from MSWI bottom ash fine fraction

In 2019, 224 Mt of Municipal Solid Wastes (MSW) were produced in Europe. A significant proportion of this MSW is treated by incineration producing each year 20 Mt of Municipal Solid Waste Incineration (MSWI) Bottom Ashes (BA). While the coarsest fraction (>2mm) can be reemployed in construction field, this is not the case for the finest fraction <2 mm (30% wt.) which is intended to be landfilled. The challenges of the treatment of this solid residue are multiple. The metals of interest are dispersed within this complex matrix and the gangue is composed by a large proportion of carbonate based minerals which reduces the choice of possible leaching agents. Moreover, the large amounts of iron and aluminum imply to choose a highly selective recovery method and the economic constrains steer the process towards low-cost technologies. The aim of this work is to study the feasibility of a selective copper and zinc recovery, whose contents in the bottom ash fine fraction are comparable to low-grade ores. A four-step process was designed consisting of a flushing, a leaching, a precipitation and an electrowinning. A selective leaching step using ammonia-ammonium chloride solution was carried out to avoid an iron co-leaching. After the leaching step, the precipitation of zinc was achieved by addition of aluminum nitrate followed by an electrodeposition of copper from ammonia medium. Up to 70% of Cu and Zn could be recovered with minimal modifications of the leachate composition allowing thus its reuse. The developed process enables the recovery of metallic copper and zinc in a spinel form from a waste originally intended for landfilling.

Efficient Recycling of Gold and Copper from Electronic Waste by Selective Precipitation.

The recycling of metals from electronic waste (e-waste) using efficient, selective, and sustainable processes is integral to circular economy and net-zero aspirations. Herein, we report a new method for the selective precipitation of metals such as gold and copper that offsets the use of organic solvents that are traditionally employed in solvent extraction processes. We show that gold can be selectively precipitated from a mixture of metals in hydrochloric acid solution using triphenylphosphine oxide (TPPO), as the complex [(TPPO)4 (H5 O2 )][AuCl4 ]. By tuning the acid concentration, controlled precipitation of gold, zinc and iron can be achieved. We also show that copper can be selectively precipitated using 2,3-pyrazinedicarboxylic acid (2,3-PDCA), as the complex [Cu(2,3-PDCA-H)2 ]n ⋅ 2n(H2 O). The combination of these two precipitation methods resulted in the recovery of 99.5 % of the Au and 98.5 % of the Cu present in the connector pins of an end-of-life computer processing unit. The selectivity of these precipitation processes, combined with their straightforward operation and the ability to recycle and reuse the precipitants, suggests potential industrial uses in the purification of gold and copper from e-waste.

Efficient Recycling of Gold and Copper from Electronic Waste by Selective Precipitation

AbstractThe recycling of metals from electronic waste (e‐waste) using efficient, selective, and sustainable processes is integral to circular economy and net‐zero aspirations. Herein, we report a new method for the selective precipitation of metals such as gold and copper that offsets the use of organic solvents that are traditionally employed in solvent extraction processes. We show that gold can be selectively precipitated from a mixture of metals in hydrochloric acid solution using triphenylphosphine oxide (TPPO), as the complex [(TPPO)4(H5O2)][AuCl4]. By tuning the acid concentration, controlled precipitation of gold, zinc and iron can be achieved. We also show that copper can be selectively precipitated using 2,3‐pyrazinedicarboxylic acid (2,3‐PDCA), as the complex [Cu(2,3‐PDCA‐H)2]n ⋅ 2n(H2O). The combination of these two precipitation methods resulted in the recovery of 99.5 % of the Au and 98.5 % of the Cu present in the connector pins of an end‐of‐life computer processing unit. The selectivity of these precipitation processes, combined with their straightforward operation and the ability to recycle and reuse the precipitants, suggests potential industrial uses in the purification of gold and copper from e‐waste.

The removal of heavy metals from refinery effluents by sulfide precipitation

This study investigated the selective precipitation of copper (Cu2+), nickel (Ni2+) and zinc (Zn2+) ions from industrial wastewater by using sodium sulfide (Na2S). The effects of pH, time and free sulfide concentration on the selective precipitation were systematically investigated using synthetically prepared solutions and gold refinery wastewater. First, the optimum precipitation pH values of metals, the amount of Na2S and time were determined by using synthetic solutions containing Cu, Ni and Zn single metal ions. The highest precipitation efficiencies were obtained at a pH of 4, 5.3 and 5.3 for Cu, Ni and Zn, respectively. Based on these results, the effects of Na2S stoichiometry and time of precipitation were investigated with synthetically prepared solutions containing mixed metal ions (100 mg/L Cu2+, 90 mg/L Ni2+ and 100 mg/L Zn2+). Metal sulfide precipitation efficiencies increased with increasing amounts of Na2S and reached a maximum at a ratio of 1:1.75 (Metal ion: Na2S molar ratio). Lastly, the results obtained from the experiments performed with synthetic solutions were used for the metal sulfide precipitation from industrial wastewater. The precipitation from refining wastewater containing 10 g/L Cu2+, 0.3 g/L Ni2+ and 3 g/L Zn2+ ions was achieved at pH values from 2.3 to 5.3. At a pH of 2.3, Cu2+ precipitated as CuS (Cu2S) at 100% efficiency. While the Ni2+ concentration in the solution decreased by only 44% at a pH of 2.3, the Zn2+ concentration decreased by 52%. At a pH of 5.3, Cu2+ and Zn2+ precipitated together at 100%.

Zinc Precipitation from Ammonia Leaching Solutions of Electric Arc Furnace Dust by Carbon Dioxide

Zinc Precipitation from Ammonia Leaching Solutions of Electric Arc Furnace Dust by Carbon Dioxide

Application of zincon analysis to investigate the zinc speciation in aqueous media for further understanding of ZnO solubility

The environmental accumulation and toxicity potential of metal oxide nanoparticles because of their increasing use in various commercial products have increased the interest in understanding the behavior of these materials in the aquatic environment. For example, zinc oxide (ZnO) is used in various industrial applications but exhibits partial solubility in aqueous media, therefore it has potential aquatoxic action. ZnO dissolves in water by releasing Zn2+ ions; thus, understanding the complexation behavior of these ions with water is crucial to be able to give a complete description of the fate of ZnO in aquatic environment. In this study, we propose application of a reliable and facile route based on the zincon analysis to further understand the Zn2+ complexation when ZnO is placed in aqueous media. To evaluate this, eight Zn2+ standards at a certain concentration were first prepared in the pH range between 7.0 and 10.0. Samples were analyzed via Inductive Coupled Plasma-Mass spectrometry (ICP-MS/MS) and the zincon analysis by monitoring their UV absorbance maximum at 620 nm. Analysis before and after centrifugation aided the investigation of the pH dependent complexation of Zn2+. In the centrifuged samples, the measured zinc ion fraction decreased, suggesting precipitation of zinc as zinc hydroxide (Zn(OH)2(s)) in the solid form from the solution when the pH was increased from 7.0 to 10.0. However, there was no significant decrease in the non-centrifuged samples in the same pH range. These results show that the zincon analysis can be used to quantify both Zn2+(aq) ions and Zn(OH)2. Moreover, the zincon results were consistent with the results of ICP-MS/MS analyses. The centrifugation helps to sediment solid hydroxide particles enabling one to predict fraction of the ions and the hydroxides. Solid hydroxide precipitate was characterized by FTIR, XRD, SEM and EDX; and formation of orthorhombic Zn(OH)2 phase was confirmed.

Comparing cyanidation with amalgamation of a Colombian artisanal gold mining sample: Suggestion of a simplified zinc precipitation process

We highlight the inefficiency of whole ore amalgamation practices used by artisanal gold miners. Cyanide is an alternative to mercury, but cleaner (cyanidation) plants are expensive and demand certain skills to operate. The main costs associated with operating a standard cyanidation plant using gold precipitation with zinc are linked to filtration, which can be costly for artisanal producers to deploy. To overcome the cost barrier, we call for the adoption of a Modified Merrill-Crowe Process (MMCP), which simplifies gold precipitation from cyanide solutions because it eliminates the need for filtration and vacuum system. Under this setup, zinc shavings in a fabric bag are introduced into the pulp of the leaching tanks with very low agitation. Lab results from a Colombian ore sample revealed that 84% of the gold was leached in 24 h with 1 g/L of CN, and over 99% of gold was precipitated in two hours. By comparison, lab amalgamation tests on the same ore using 28 times more mercury used by artisanal miners yielded less than 19% gold recovery.

Физико-химическое моделирование системы ZnSO4-CaO(MgO)-SiO2-H2O

The paper presents the results of zinc precipitation from sulfate solutions with alkaline reagents (serpentinite magnesite and calcium oxide). X-ray diffraction, micromorphological analysis, and thermodynamic modeling revealed the formation of stable metastable silicate zinc-containing phase in the experiment with the use metaserpentine as a reagent. When calcium oxide is used as a reactant, zincite precipitated.

Cost-Effective and High Purity Valuable Metals Extraction from Water Leaching Solid Residues Obtained as a By-Product from Processing the Egyptian Boiler Ash

The water leaching solid residues (WLSR) obtained from salt-roasting Egyptian boiler ash are considered an essential secondary resource for (13%) nickel and (5.6%) zinc extraction. Hence, the current study aims for the cost-effective and high purity Ni, Zn, Fe and Mg metal ion extraction from (WLSR) using a sulfuric acid leaching process. The factors affecting the percentage recovery of Ni, Zn, Fe and Mg from WLSR, including leaching temperature, time, acid concentration and solid/liquid ratio, have been investigated. The obtained leaching solutions were analyzed chemically using ICP, and the different precipitates were analyzed mineralogically using XRD and EDX analysis and chemically using XRF. The maximum percentage recovery of Ni, Zn, Fe and Mg was 95.02%, 90.13%, 66.29% and 75.73%, which was obtained under the optimum leaching conditions of 8% H2SO4 concentration and 1/15 solid/liquid ratio at 85 °C for 240 min. The effect of pH, Fe2O3 dosage as nucleating agent and the precipitation duration on iron removal and Ni and Zn loss have been thoroughly studied. It has been found that &gt;95% of the contained iron impurity can be removed, while nickel and zinc losses are around 4.2% and 3.8%, respectively. Additionally, a pH of 6 and 0.45 mol/L concentration of H2C2O4 was utilized to precipitate Mg as MgC2O4.2H2O, demonstrating that the precipitation efficiency of Mg reaches 96.9%. Nickel and zinc precipitation efficiency was 92.25% and 85.51%, respectively, by raising the solution pH to approximately 9. The kinetic of Ni and Zn dissolution has been investigated to explain the mechanism prevalent and the factors influencing the leaching process. It has been found that the nickel leaching kinetic is controlled by both diffusion through an inert porous layer and by chemical reaction with an activation energy of 20.25 kJ.mol−1. Meanwhile, the kinetic of zinc leaching is controlled by solid product layer diffusion with an activation energy of 11.67 kJ mol−1.

Studies of Selective Recovery of Zinc and Manganese from Alkaline Batteries Scrap by Leaching and Precipitation.

Recovery of zinc and manganese from scrapped alkaline batteries were carried out in the following way: leaching in H2SO4 and selective precipitation of zinc and manganese by alkalization/neutralization. As a result of non-selective leaching, 95.6–99.7% Zn was leached and 83.7–99.3% Mn was leached. A critical technological parameter is the liquid/solid treatment (l/s) ratio, which should be at least 20 mL∙g−1. Selective leaching, which allows the leaching of zinc only, takes place with a leaching yield of 84.8–98.5% Zn, with minimal manganese co-leaching, 0.7–12.3%. The optimal H2SO4 concentration is 0.25 mol∙L−1. Precipitation of zinc and manganese from the solution after non-selective leaching, with the use of NaOH at pH = 13, and then with H2SO4 to pH = 9, turned out to be ineffective: the manganese concentrate contained 19.9 wt.% Zn and zinc concentrate, and 21.46 wt.% Mn. Better selectivity results were obtained if zinc was precipitated from the solution after selective leaching: at pH = 6.5, 90% of Zn precipitated, and only 2% manganese. Moreover, the obtained concentrate contained over 90% of ZnO. The precipitation of zinc with sodium phosphate and sodium carbonate is non-selective, despite its relatively high efficiency: up to 93.70% of Zn and 4.48–93.18% of Mn and up to 95.22% of Zn and 19.55–99.71% Mn, respectively for Na3PO4 and Na2CO3. Recovered zinc and manganese compounds could have commercial values with suitable refining processes.

Friction Stir Welding of Aluminum 7075 Alloys

Abstract: Friction Stir Welding (FSW) is a solid-state welding method which was developed by The Welding Institute and patented in 1999. The process is solid state and relies on local forging of weld region to perform weld. New welding schedules are being continuously developed for materials that are traditionally difficult to join by fusion welding methods (e.g., TIG/MIG). These experiments are performed to find out the best possible parameters to smoothly weld the aluminium 7075 alloys. By using Taguchi robust design of experiment, we selected 3 parameters namely rotation speed and transverse speed and tool shoulder diameter against the optimization function of ultimate tensile strength. The tilt angle and the plunge depth are kept constant. The variation of tensile strength is mainly due to the change in tool shoulder diameter then with welding speed and then with rotation speed. The heat generated is modelled on ANSYS software by inserting the rotation speed, coefficient of friction , material properties , radius of pin etc. The model is validated by conducting the experiment through thermocouples. The model predicted a temperature of about 410 degrees Celsius and the experimental value is 380 degrees Celsius, showing that the welding temperature is about 80% of heat generation. The Taguchi experiment consist of 4 experiments with a range of rotation speeds of 900 and 1120 respectively and a welding speed of 64mm/min and 100 mm/min respectively. The tool shoulder diameter is kept 14mm and 17mm. the welds are cut in transverse direction in order to obtain the UTS test coupon. The best possible combination is found using Taguchi Analysis. This thesis is a collection of data and response variables that correctly informs at what conditions we should weld 7075 alloy. Appropriate SN ratio is calculated and high is the best is considered as our objective function is tensile strength. Some additional tests are also performed namely hardness and microstructure and heat generation in order to identify the behaviors of aluminium alloy. Hardness and heat generated are dependent on the tool shoulder diameter then on the welding speed. This conclusion is derived from Taguchi analysis. This study is useful for the selection of parameters for the further welding operations. However, a change in plunge depth can also be taken into consideration for future scope. As tunneling defect was observed in some runs thus plunge depth has to be varied. Also, the number of experiments can be increased in order to get more refined parameters. Also, the making of base material can also be taken into consideration because of the zinc precipitate distribution. Casted AA7075 has different properties, rolled AA 7075 can have different.

Enabling a stable and dendrite-suppressed Zn anode via facile surface roughness engineering

• Smoother zinc metal anode surface exhibits better hydrophilicity. • Smoother zinc metal anode surface exhibits lower potential barrier and faster reaction kinetics. • Monitoring anode surface electrochemical behaviors during charging. • Computational simulation of the relationship between surface roughness and battery performance. The safety and cycle lifespan of zinc metal-based aqueous batteries are greatly restricted by zinc anode. The poor cycling performance of zinc metal anode is often considered to be impacted by the dendrite growth, surface passivation, zinc metal corrosion and hydrogen evolution reaction, while surface roughness is a matter that has often been ignored in past studies. Herein, a roughness gradient is constructed on the zinc anode surface by a simple grinding and pasting method. It has been found the modified zinc anodes with lower surface roughness exhibit the smaller zinc deposition overpotential and longer cycle life. Further, in situ optical microscopy photographs indicate that the zinc anode with an optimized roughness enables more uniform distribution of zinc precipitation and corrosion sites, which will facilitate a stable cycling performance of aqueous zinc ion batteries. The Zn anode dendrite-suppressing mechanism via surface roughness engineering was revealed through finite element computational simulation. These results emphasize the effectiveness of roughness engineering for tuning the surface physics of Zn anode and provide a facile strategy to develop better and safer aqueous zinc ion batteries.

Laboratory-Scale Bio-Treatment of Real Arsenic-Rich Acid Mine Drainage

Acid mine drainage (AMD) still represents a huge environmental problem. Technical and scientific breakthroughs are still needed to decrease environmental damages, treatment cost, and waste production associated with AMD. The feasibility of combining continuously fed anaerobic sulfate-reducing bioreactor with downstream iron oxidation step was tested, at a laboratory scale, with two types of real arsenic-rich AMD waters from the site of Carnoulès (France), that differed in acidity (pH 3.3 and 4.0), arsenic (As, 18 and 174 mg.L−1), and metal concentrations. Iron remained in solution, while up to 99% of As was precipitated as amorphous orpiment in the anaerobic sulfate-reducing bioreactor. Zinc (Zn) precipitation was also observed, up to 99%; however, the efficiency of Zn precipitation was less stable than that of As. The anaerobic bioreactor presented a stable bacterial community including a Desulfosporosinus-related sulfate reducer. When the effluents from the anaerobic process step were treated in a laboratory aerobic bioreactor, iron was oxidized efficiently. The feasibility of efficient orpiment bio-precipitation coupled with downstream iron oxidation was shown, thus opening the perspective of a low-cost combination of treatment steps for the removal of arsenic, zinc, and iron in As-rich AMDs.

Pigments from spent Zn, Ni, Cu, and Cd electrolytes from electroplating industry.

One of the problems of electroplating industry is the periodic discharge of concentrated spent electrolytes together with rinsing wastewater. This leads to irreversible loss of valuable components, as well as to the risk of heavy metal ions entering the environment, which have toxic, mutagenic, and carcinogenic effects. The paper presents research on the processing of spent electrolytes from electroplating industry of zinc, nickel, copper, and cadmium plating, collected over 3 years. Pigments of various colors were obtained by precipitation of zinc, nickel, copper, and cadmium ions by phosphate, hydroxide, and sodium carbonate. By their properties, i.e., whiteness 95-97%, residue after sieving on a sieve up to 0.04 wt.%, etc., the resulting pigments are not inferior to those currently presented on the world market. Following previous studies, a basic technological scheme for processing waste electrolytes with pigments production is proposed. Processing of spent electrolytes according to the proposed technology will make it possible to reduce the concentration of heavy metal ions to acceptable values (0.13-0.65 mg/L) for discharge. This will ensure stable and uninterrupted operation of local treatment facilities of electroplating industry.

The precipitation synthesis of zinc (II) oxide for photocatalytic degradation of anionic and cationic dyes

The method of zinc (II) oxide synthesis by precipitation of zinc (II) acetate precursor has been developed. With the method of scanning electron microscopy, it was found that ZnO particles have a size of less than 100 nm. It contains a pure phase of zinc (II) oxide of the hexagonal syngony of the wurtzite type, which was proved by the X-ray diffraction method. The absorption spectrum of suspension of the obtained zinc (II) oxide powder was obtained and the optical bandgap was calculated by the Kubelka–Munk formula. The synthesized zinc (II) oxide is a well-crystallized solid material with semiconductor properties and a clear bandgap, starting at 3.1 eV. The resulting zinc (II) oxide has a BET surface area of 22 m2/g, as a result of which, its total porosity and micropore volume are small: 0.13 cm3/g and 0.06 cm3/g, respectively. It confirms that the obtained ZnO is a well-crystallized, non-porous material. The photocatalytic activity of the synthesized zinc (II) oxide is very high towards the dyes of both, anionic and cationic natures. The experimentally achieved values of the photocatalytic decomposition degree of the studied dyes indicate to an ambiguous influence of the model photocatalytic process organization on the efficiency of ZnO.