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To realize the high value-added utilization of zinc hypoxide in a rotary hearth furnace, nano-ZnO was prepared by H2SO4 wet leaching combined with the Na2CO3 precipitation process. The effects of different process conditions on the leaching rate of Zn were analyzed, and the feasibility of preparing nano-ZnO from zinc hypoxide was discussed. The results showed that the optimal process conditions for H2SO4 leaching of zinc hypoxide in a rotary hearth furnace were as follows: H2SO4 concentration 2.0 mol·L−1, leaching temperature 60 °C, leaching time 90 min, and liquid-solid ratio 8:1. Under these conditions, the leaching rate of Zn reached 95%. The calculation results of leaching kinetics showed that the restrictive link of the H2SO4 leaching process was a chemical reaction process; the apparent activation energy was 14.45 kJ·mol−1; and the reaction order was 0.6. The precursor obtained by Na2CO3 precipitation treatment was Zn5(OH)6(CO3)2. After calcination at 400 °C, the nano-ZnO with a diameter of less than 100 nm and length greater than 1 μm was obtained. H2SO4 leaching combined with the Na2CO3 precipitation process provided a new approach for high value-added utilization of zinc hypoxide in a rotary hearth furnace.

Green, efficient, and cost-effective soil leaching technologies have emerged as an innovative strategy for remediating heavy metal-contaminated soils. In this study, we proposed NH 4 HSO 4 and KHSO 4 as novel eluents for removing heavy metals from contaminated soils and investigated the effects of various factors, including leaching temperature, liquid to solid ratio (L/S), time, and molar concentration ratio, on their efficacy. We also examined the mineral contents and structural properties of the contaminated soil before and after leaching using the novel eluents via scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy, and Fourier transform infrared spectroscopy. The results indicated that the leaching rates of Zn, Pb, and Cd using NH 4 HSO 4 and KHSO 4 (25 °C, 360 min, L/S = 20, and 0.075 mol/L) were 86.17%, 45.97%, and 79.92% and 89.12%, 46.185%, and 84.32%, respectively. Furthermore, these eluents improved the quality of the treated soil by slightly increasing its N and K contents without altering its structure. The leaching rates of Zn in the exchangeable and acid-soluble, reducible, and oxidizable forms by KHSO 4 were best fitted by the Avrami–Erofeev equation, diffusion via the product layer, and the new shrinking core model, respectively. The heavy metal proportion in the oxidizable and residual fraction increased after leaching. Based on these findings, NH 4 HSO 4 and KHSO 4 show promise as effective agents for the rapid, efficient, cost effective, and sustainable remediation of heavy metal-polluted soils.

Purpose Re-vegetation is the preferred long-term practice for managing Alcoa's bauxite-processing residue storage areas. Residue sand is the primary growth medium for rehabilitation; however, it is largely nutrient deficient. Although addition of organic and inorganic amendments can provide short-term supply of plant-available nutrients, but quickly exhausted, thus long-term deficiencies are often observed. The rapid transformation of added zinc into non-available pools is predicted as the main factor limiting vegetation performance. Materials and methods Two laboratory investigations were carried out to assess the effect of organic (composts) and inorganic (various types of red mud) amendments on Zn availability in residue sand. Three compost mixtures (piggery, biosolid and commercial compost), three rates of application (0, 10 and 50 t ha⁻¹) were taken as organic amendments and incubated with residue sand for 30 days to examine the effects of compost on Zn availability. Seven column treatments were set up as: control residue sand, homogeneous mixtures of residue sand with 3% (w/w) and 8% (w/w) seawater-washed, carbonated or unaltered red mud with residue sand. Leaching with distilled water was carried out every 3 days by adding 1/6th pore volume and analysed for Zn availability and its distribution in various chemical pools. Results and discussion Fractionation studies found that Zn availability decreased with incubation time and red mud amendments. Residue pH and organic C were the major factors controlling Zn availability and its distribution. Column studies showed limited Zn mobility in residue sand even after three pore volumes of drainage. Increased DTPA extractable Zn in surface layers of residue sand with and without red mud amendments after leaching was found and attributed to decrease in residue water-soluble alkalinity. Addition of commercial compost (50 t ha⁻¹) increased DTPA Zn, decreased the alkalinity and increased C content in residue sand. The red mud amendments had contrasting effects on Zn that were related to pH of the materials. Addition of seawater-washed red mud increased DTPA Zn in residue sand whereas unaltered red mud decreased DTPA Zn. Conclusions Plant available Zn extracted with 50 t ha⁻¹ of commercial composts addition was well above deficient range, suggesting that they could be an effective Zn source for vegetation establishment. Zinc occurred predominantly in organically bound form in compost-amended sand and as carbonate-bound form in leached red mud-amended columns, but the longer term effects of these Zn forms on the release of Zn for plant growth remain unclear.

A greenhouse experiment was conducted on weakly acidic and calcareous soils to evaluate the aging and residual effects of three natural organic Zn chelates [Zn-ethylenediaminedisuccinate (Zn-EDDS), Zn-polyhydroxyphenylcarboxylate and Zn-aminelignosulfonate] each administered in a single application to a first navy bean (Phaseolus vulgaris L.) crop at several different Zn application rates. In a second navy bean crop, we determined the following parameters: the extent of Zn leaching, the amount of available Zn remaining in soils, the amount of easily leachable Zn, the size of Zn fractions in soils, the pH and redox potential, the dry matter yield, and the soluble and total Zn concentrations in plants. The residual effect after 2 years of Zn fertilization mainly depended on the aging effect of Zn chelates and losses due to Zn leaching. The data relating to the evolution from the first to the second crop showed that the aging effect was noticeable in the calcareous soil. In the latter soil, the Zn-S,S-EDDS treatments showed greater decreases in the Zn uptake by plants than the other Zn treatments and the greatest Zn uptake by plants occurred when Zn was applied as Zn-aminelignosulfonate (10 mg Zn kg⁻¹ rate, 6.85 mg Zn per lysimeter; 5 mg Zn kg⁻¹ rate, 3.36 mg Zn per lysimeter). In contrast, in the calcareous soil, the maximum amount of Zn uptake, for the three chelates was 0.82 mg Zn per lysimeter. Consequently, a further application of Zn would be needed to prevent Zn deficiencies in the plants of a subsequent crop. The behaviour of the pH and Eh parameters in the soils and leachates did not depend on the natural Zn sources applied. In this study, the easily leachable Zn estimated by BaCl₂ extraction was not adequate to predict Zn leaching from the soils in subsequent crops.

Eight soils from the Gulf of Kalloni in Lesvos Island, Greece, most of which were of low clay and low organic matter content, were used in a series of leaching experiments. The aim was to investigate the role of sewage sludge on Zn leaching and determine the soil properties that affect it. It was found that sludge addition at a low application rate (10 t ha⁻¹) decreased Zn leaching significantly by 30%. From a regression analysis it was found that eluted Zn was reduced with increasing Fe oxides content, probably due to Zn adsorption onto them, and that Zn transport increased with clay content. This indicates that Zn leaching was facilitated by the downward movement of clay particles, which was also suggested by the erratic Zn breakthrough observed in many soils. This was further confirmed by the fact that colloid concentrations increased with clay content in the soils (R = 0.85, P < 0.05). The results show that the addition of sewage sludge to low organic matter and clay content soils at moderate application rates enhances soil organic carbon and increases metal retention capacity.