Recovering Zinc from electroplating wastewater by crystallization in a pellet reactor

A pellet reactor (PR) was used to investigate the ability for zinc recovery from electroplating wastewater. The pellet reactor is a fluidized bed reactor, in which the nucleated precipitation of heavy metals occurred on the surface of seeding material. The zinc removal efficiency was 75% at molar ratio [CO3 2-]/[Zn2+] of 2.5, the flowrate of 16 L/h, sand’s diameter of 0.25 – 0.5 mm, and sand’s mass of 50 g. The elemental analysis of zinc carbonate and zinc hydroxide crystallization was analyzed by X-ray energy dispersive spectrometer (EDS) and the surface was characterised by Scanning electron microscope (SEM) to get the morphological observation of the pellets after 38-day operation. This study demonstrated that the fluidized bed reactor can be considered a feasible method for zinc removal efficiency from electroplating wastewater to achieve sustainable development.

The determination of synthesis conditions and color properties of pigments based on layered double hydroxides with Co as a guest cation

Nail polish, in particular gel polish, is the most commonly used cosmetic product. A component of the gel polish, which determines the consumer color characteristics of the gel polish. Layered double hydroxides (LDH) are promising pigments. To expand the range of colors and shades of pigments, the use of LDH with colored host and guest cations is promising. The parameters of synthesis and color characteristics of samples of Zn-Co and Cu-Co hydroxide pigments were studied. To obtain LDH with Co as a guest cation in the synthesis, the conversion of cobalt to the trivalent state was carried out at a temperature of 80 °C using oxidation with atmospheric oxygen or sodium hypochlorite. The oxidation efficiency was evaluated by X-ray phase analysis by the presence or absence of cobalt-containing phases. The color characteristics of the synthesized pigment samples were studied by spectroscopic measurement and calculation in RGB, CIELab, and LCH color models. The low efficiency of cobalt oxidation at the moment of Zn-Co LDH synthesis with atmospheric oxygen at an elevated synthesis temperature of 80 °C was shown, while cobalt was released as a separate Co3O4 phase. A higher efficiency of cobalt oxidation at the moment of synthesis using sodium hypochlorite with the formation of Zn-Co LDH was revealed. It is recommended to use the hypochlorite oxidation of Co2+ to Co3+ in the LDH synthesis with Co in the form of a guest cation. The formation of a separate phase of zinc oxide was found in both types of oxidation due to the thermal decomposition of zinc hydroxide. Comparative analysis of color characteristics showed that all samples have a brown color of different saturation. It was revealed that during the formation of Co-containing LDH, the lightness of the color decreases. Color saturation increases in the case of a colored host cation, such as Cu.

Carboxymethyl Cellulose Hydrogel Based Formulations of Zinc Hydroxide Nitrate-Sodium Dodecylsulphate-Bispyribac Nanocomposite: Advancements in Controlled Release Formulation of Herbicide

The usefulness of carboxymethyl cellulose (CMC) as a matrix material in enhancing the controlled release formulations of bispyribac (BP) herbicide from the interlayer gallery of zinc hydroxide nitratesodium dodecylsulphate–bispyribac (ZHN–SDS–BP) nanocomposite was investigated. The CMC coated nanocomposite, ZHN–SDS–BP–CMC was characterised using several instruments for the determination of its physicochemical properties. The release rates of the BP were measured using a UV spectrophotometer, and the aqueous solutions containing PO3−4 , SO2−4 and Cl− were selected as release media in the release studies so as to mimic the real conditions of environmental soil. Significant release time delays, triggered by the gelation forming ability and hygroscopic nature of CMC, were observed in all release media, and the release processes were found to behave in a concentration-dependent manner in all release media. Fitting the release data into several kinetic models demonstrated that release in aqueous solutions of Na3PO4 and Na2SO4 was governed by pseudo second order processes, whereas the release in an aqueous NaCl solution was governed by the parabolic diffusion kinetic model. The potential of CMC in prolonging the release of BP from ZHN–SDS–BP–CMC can potentially help in reducing the pollution resulting from the overuse of pesticides.

Semiconductor metal oxide sensor for hydrogen sulphide operating under non-stationary temperature conditions

The aim of the work was to create a selective gas sensor for hydrogen sulphide. As a result of adding ammonia to the zinc acetate solution, centrifuging the obtained zinc hydroxide and subsequent calcination, a polydisperse zinc oxide powder with a grain size of 5–50 nm was obtained. The material was characterized using X-ray phase analysis and transmission electron microscopy. Subsequently, silver nitrate and terpeniol were added to the zinc oxide nanopowder to form a paste. The gas-sensitive material was obtained by applying the resulting paste on a special dielectric substrate and subsequent calcination, as a result of which the terpeniol burned out, and the silver nitrate turned into an oxide (the mass fraction of the silver was 3%). A non-stationary temperature mode for the operation of the sensor was selected, in which, after rapidheating of the sensor to 450 °C (2 seconds), slow (13 seconds) cooling to 100 °C occurred. Each subsequent heating-cooling cycle with a total period of 15 seconds began immediately after the end of the previous cycle. The use of an unsteady temperature mode in combination with the selection of the composition of the gas-sensitive layer made it possible to obtain a response of 200 for a hydrogen sulphide concentration of 1 ppm. Along with an increase in sensitivity, a significant increase in selectivity was also observed. The cross-sensitivity for the determination of hydrogen sulphide and other reducing gases (CO, NH3, H2) was more than three orders of magnitude. Thus, this sensor can be used to detect hydrogen sulphide even in the presence of interfering components. The use of highly selective sensors in the tasks of qualitative andquantitative analysis can significantly simplify the calibration in comparison with “electronic nose” devices. Devices based on highly selective sensors do not require the use of mathematical methods for processing multidimensional data arrays.

Synthesis and properties of nanosized ZnO/wood composite

The aim of the study was to synthesise a ZnO/silver birch wood (Bétula péndula) nanocomposite and evaluate its physical and mechanical properties in comparison with an unmodified natural polymer.Using the sol-gel method, we synthesised almost spherical impurity-free zinc oxide nanoparticles with a predominant particle size of about 20 nm. Amorphous hydrated Zn(OH)2 was impregnated into the wood material at the gel formation stage. It resulted in the reaction of zinc hydroxide decomposition with the formation of ZnO nanoparticles in the wood as a nanoreactor.The hydrophobic properties of the surface of ZnO/silver birch wood nanocomposite improved significantly (the contact angle of wetting doubled). Its moisture and water resistance decreased (2-5 times and 30%, respectively). The nanocomposite also showed less swelling in the radial (8-10 times) and tangential (2.6-10 times) directions in comparison with natural wood.

ZIF-8 Coupling with Reduced Graphene Oxide to Enhance the Electrochemical Sensing of Dopamine

A reduced graphene oxide@zeolitic imidazolate framework-8 (rGO@ZIF-8) based electrochemical sensor was developed and used for dopamine detection. ZIF-8 was rapidly prepared by zinc hydroxide nitrate (Zn-HDS, Zn5(OH)8(NO3)2·2H2O) as precursor. Subsequently, rGO was introduced to enhance the performance of ZIF-8 (e. g., high carrier mobility, favorable stability), and a label-free electrochemical dopamine sensor based on the composite material was obtained with high specific surface area and better conductivity verified by Brunauer-Emmett-Teller surface analysis and electrochemical impedance spectroscopy, respectively. Consequently, rGO@ZIF-8 complex exhibited an admirable electrochemical catalytic performance. For determination of dopamine, the sensor behaves wide linear range from 2.0 x 10-6 to 1.4 x 10-4 mol/L and lower detection limit of 2.0 x 10-8 mol//L (S/N = 3). It also showed sufficient repeatability and durability due to the coordinated amplification effect of rGO and ZIF-8.

Demulsification Behavior of Alkali and Organic Acid in Zinc Extraction

Alkali agents could be used to enhance the extraction of zinc from solution of high concentration, but excess alkali can sensitively lead to emulsification of the solution. In this paper, the emulsification in the extraction process, demulsification, and extraction with different additives and its action mechanism were studied. The results indicate that the associated addition of alkali and organic acid could eliminate emulsification and improve zinc extraction. The extraction ratio of zinc reached 99.61% under the conditions of 104 mL/L organic acid, 80 g/L alkali, and 40% extractant concentration. Zinc hydroxide formed from hydroxyl and zinc ion at sensitively increased pH was the cause of emulsification during extraction. Associated addition of alkali and organic acid could contribute to the control solution pH in the range of 3.0–4.0, which is lower than that of the formation of zinc hydroxide, and therefore, improve zinc extraction.

Reaction mechanisms for electrolytic manganese dioxide in rechargeable aqueous zinc-ion batteries

This study reports the phase transformation behaviour associated with electrolytic manganese dioxide (EMD) utilized as the positive electrode active material for aqueous zinc-ion batteries. Electrochemical techniques, including galvanostatic charge–discharge and rotating ring-disk electrode measurements, and microstructural techniques, using X-ray powder diffraction, scanning electron microscopy, and transmission/scanning transmission electron microscopy, were utilized to characterize the positive electrode at different stages of discharge and charge of zinc-ion cells. The results indicate that, during discharge, a fraction of EMD undergoes a transformation to ZnMn2O4 (spinel-type) and Zn2+ is intercalated into the tunnels of the γ- and ε-MnO2 phases, forming ZnxMnO2 (tunnel-type). When a critical concentration of Mn3+ in the intercalated ZnxMnO2 species is reached, a disproportionation/dissolution reaction is triggered leading to the formation of soluble Mn2+ and hydroxide (OH–) ions; the latter precipitates as zinc hydroxide sulfate (ZHS, Zn4(OH)6(SO4)·5H2O) by combination with the ZnSO4/H2O electrolyte. During charge, Zn2+ is reversibly deintercalated from the intergrown tunneled phases (γ-/ε-ZnxMnO2), Mn2+ is redeposited as layered chalcophanite (ZnMn3O7·3H2O), and ZHS is decomposed by protons (H+) formed during the electrochemical deposition of chalcophanite.