Leaching Cycle Research Articles

Hydrometallurgical processing of spent zinc-manganese batteries

This paper explores the possibility of zinc-manganese battery recycling in alkaline solutions. It was shown that three-stage washing could remove potassium chlorides from active mass of milled batteries. Influence pattern regularities were established for some parameters (temperature, alkali concentration and number of cycles) of alkaline leaching of a zinc-carbon and alkaline battery mixture in respect of zinc extraction into the solution. The reason of low zinc extraction from this material was found to be the presence of zinc and manganese compounds as heterolite and hydroheterolite that are difficult to dissolve in alkalis. It was found that zinc extraction increases by 2.6 times with an increase in the NaOH concentration from 100 to 205 g/dm 3 , but further increase in the NaOH concentration, as well as an increase in temperature in the range of 30–85 °C, does not affect zinc extraction into the solution. Optimal process parameters of zinc-carbon and alkaline battery leaching at 30 min leaching time and 200 g/dm 3 pulp density were determined as follows: temperature is 30 °C, NaOH concentration is 390 g/dm 3 . Experiments on zinc ion accumulation with repeated filtrate leaching showed that increasing the initial NaOH concentration to 390 g/dm 3 makes it possible to transfer the maximum possible amount of zinc into the solution at the same NaOH consumption due to the cyclic treatment of solutions. Zinc and NaOH concentrations in solutions after leaching reached 59 g/dm 3 and 300 g/dm 3 , respectively. Solutions obtained could be sent to zinc electrowinning and then returned to leaching again.

Effect of silica bionanoparticles obtained from rice husk for the treatment of wood of Pinus elliottii

Renewable products can ensure environmental sustainability, human health, and reduce the use of traditional products that have toxic compounds in their formulation. Therefore, the research aimed to evaluate the biological resistance of Pinus elliottii wood against xylophagous fungi and termites through impregnation with silica bioparticles (SiO2) obtained from rice husks. To obtain the silica, the material underwent chemical treatment, two cycles of acid leaching with hydrochloric acid, and heat treatment at 500 °C, 550 °C or 600 °C. The purity of the silica obtained was characterized by X-ray fluorescence technique (XRF), and the mean particle size by scanning electron microscopy (SEM). SiO2 was applied to the specimens at concentrations of 0.5%, 1.0%, and 2.0%, and the impregnated samples were subjected to tests with brown rot fungi (Gloeophyllum trabeum, Rhodonia placenta and Neolentinus lepideus), soft rot (taken from natural forest soil) and xylophagous termites (Nasutitermes corniger and Cryptotermes brevis). The thermal treatments promoted the obtainment of high purity bioparticles, with value of approximately 90% and diameter of 263.7 nm. In the termite test, the smallest loss of mass and damage were for the impregnated samples. Termite mortality increased with the concentration of solutions. SiO2 was not effective against xylophagous fungi, with no difference between treatments and controls, indicating that resistance was inherent in the wood itself.

Properties of Mexican bloodwood (Haematoxylum campechianum L.). Part 1: anatomical and colourimetric characteristics

Abstract Bloodwood (Haematoxylum campechianum L.) native to Central America has been known as dye source since the prehistoric times by the Maya. Nowadays, bloodwood is increasingly used for plantations but its use for furniture, flooring, or fencing is only of regional importance. The reason is seen in lacking knowledge of its properties. To expand that knowledge, this Part 1 of the two-part study series investigated the anatomy and the discolouration due to leaching of heartwood of H. campechianum. Anatomical characteristics were described qualitatively and quantitively using scanning electron microscopy and X-ray micro-computed tomography. Detailed wood anatomical data are presented, together with numerical analyses of cell parameters. Apart from wood anatomy, colourimetric analyses were obtained after 10 leaching cycles. The colour change of the wood due to water exposure was determined measuring in CIE L*a*b* colour system. In addition, the extinction of the leachate was determined spectrophotometrically after each leaching cycle. The resulting colour change was evaluated according to colour change after each cycle. The most prominent change in colour was observed for the first cycle due to leaching. Because of the extensive leaching of extractives, further investigation might address the effect of leaching of water-soluble extractives on adhesion properties of bloodwood.

Utilization of phosphogypsum waste through a temperature swing recyclable acid process and its application for transesterification

In this paper, a biodiesel catalyst was prepared from the phosphogypsum (PG) by a hybrid approach through temperature swing acid leaching/crystallization steps followed by the subsequent fluidized bed calcination. The impacts of acid leaching and crystallization were extensively analyzed via a supervised machine learning approach using a limited number of experimental runs to find out the optimal condition. The determined optimal conditions are X1-95 (ºC), X2-30 (min), X3-30 (wt%-H2SO4), and corresponding validation experimental result (at the optimal condition setting) shows± 5% uncertainties. The prepared catalyst predominately contains CaSO4 (98 wt%) with the impurities less than 0.3 wt% (i.e., P2O5- and F-). The numbers of acid leaching cycles (up to 10 cycles) were investigated, and result indicates a good contaminates recovery (P2O5:1.8 g/100 g PG, Mg2+: 0.3 g/100 g PG, Al3+: 0.3 g/100 g PG, Fe3+: 0.1 g/100 g PG) in the leachate through the downstream solvent extraction. The catalytic conversion reaches about 50% with approximately± 5% deactivation when catalyst was reused at the same transesterification condition. The decreased binding energies of S2p (169.6 eV) and O1st (533 eV) in used catalyst indicate the deactivation of surface catalytic sites. The key properties of the prepared biodiesel are comparable to the American society for testing and materials (ASTM) standards.

Phylogenetically divergent bacteria consortium from neutral activated sludge showed heightened potential on bioleaching spent lithium-ion batteries

Recycling of spent lithium-ion batteries (LIBs) has become a global issue because of the potential environment risks raised by spent LIBs as well as high valuable metal content remaining in them. Although bioleaching is an environmentally friendly method to recover metals from spent LIBs, the commonly utilized bioleaching bacterial consortia or strains enriched/isolated from acidic environments cannot be applied at large scales owing to their long leaching cycle and poor tolerance to organic compounds. Here, two bioleaching consortia were enriched in 60 days from neutral activated sludge and were identified phylogenetically divergent from the documented bioleaching bacteria. The results showed that the novel consortia shortened the leaching cycle almost by half when compared to the previous reported consortia or strains, of which one consortium dominated by Acidithiobacillus ferrooxidans displayed high bioleaching efficiency on LiMn2O4, as 69.46% lithium (Li) and 67.60% manganese (Mn) were leached out in seven days. This consortium was further domesticated using cathodic materials for 100 days and proved consisted of three mixotrophs and two chemoautotrophs, three of which were novel species from the genera Sulfobacillus and Leptospirillum. More genes coding for proteins that utilize organic compounds were annotated in the metagenomic assembled genomes (MAGs) than previously reported. A mutualistic relationship between mixotrophs and chemoautotrophs was suggested to help the consortium surviving under either organic- rich or shortage environments. The results discovered that novel bioleaching bacteria with shorter leaching cycle and higher tolerance to organics could be enriched from non-acidic environments, which showed high potential for the metal recovering from spent LIBs or other organic-rich environments.

The effect of temperature and digested sewage sludge cover over tailings on the leaching of contaminants from Ballangen tailings deposit

Abstract Dry covers can be applied above tailings to reduce and prevent formation of acid mine drainage and leaching of contaminants. Efficiency of covers is affected by different parameters, of which temperature change under climate change context is one. Here, a laboratory column leaching experiment was performed under four temperatures, 5, 10, 14, and 18 °C on unoxidized tailings from Ballangen, Norway. 600 mL of water was added to each column every second week and leachate was collected and analyzed for pH, salinity, alkalinity, concentrations of sulfate, Co, Fe, Mn, Ni, and Zn. A thin layer of digested sewage sludge was added to columns after the 16th leaching cycle. In total, 21 leaching cycles were performed. Results showed low oxidation of tailings and therefore high pH and low salinity, SO42−, Fe, Ni, and Co in the leachates at leaching temperature of 5 °C. Addition of sludge cover slowed down oxidation of underlying tailings and decreased leaching of SO42−, Fe, Mn, Co, Ni, and Zn from the tailings deposit, especially at relatively high temperatures. 10 °C is a threshold temperature, below which leaching is not affected by the cover addition so much. At a leaching temperature higher than 10 °C, the sludge cover addition can reduce the leaching of elements significantly.

Wood modification with N-methylol and N-methyl compounds: a case study on how non-fixated chemicals in modified wood may affect the classification of their durability

Abstract Chemical modification is increasing the durability of wood against biological deterioration. Usually, the effect of a new treatment on the durability of wood is screened in laboratory decay tests, where durability classes are assigned on the basis of the mass loss (ML) caused by degrading fungi. The aim of this study was to demonstrate how non-fixated chemicals in modified wood may affect fungal ML measurements and corresponding durability classification when wood samples are incubated under humid conditions for long periods. Wood blocks were treated with solutions of 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU), methylated DMDHEU (mDMDHEU) and 1,3-dimethyl-4,5-dihydroxyethyleneurea (DMeDHEU) and subjected to consecutive cold-water leaching cycles. Significant amounts of non-fixated chemicals were removed from the wood by three leaching cycles and might lead to ML mistaken as response of fungal decay. Consequently, the treated material was assigned erroneously by up to four durability classes (DC) worse than material which did not include leachable, non-fixated chemicals. Thus, for a reliable durability classification of chemically modified wood, prolonged leaching procedures are recommended to assure that the measured ML is entirely attributed to fungal decay.

Assessment of dendrocalamus asper (Schult and schult f.) (Poaceae) bamboo treated with tannin-boron preservatives

• Acacia mearnsii tannin successfully cross-linked with hexamine and boron. • Tannin-based preservatives improved fungi decay resistance of bamboo. • Superior mechanical properties obtained with tannin-boron treatment. • Boron compounds and tannin positively affected the thermal stability of bamboo. Tannin-boron based preservative solutions were used for the treatment of D. asper bamboo by vacuum/pressure impregnation. Samples treated with tannin/hexamine-based solutions presented low weight losses after decay tests with P. sanguineus and G. trabeum decay fungi, and were classified as resistant and highly resistant, respectively, even after leaching. However, a high boron loss after severe leaching cycles was observed. Samples treated with tannin/hexamine/boron had superior mechanical properties and increased thermal stability. The use of tannin-based solutions in combination with boron compounds showed promising results in terms of mechanical properties improvement and increased fungal decay resistance, bringing new possibilities for bamboo preservation.

Beech wood impregnation with hydrolyzed wattle tannin

Tannins and their toxic effects against various decay organisms have been interrelated for centuries. As natural products have gained more interest, waste from several production fields abundant in tannins has yielded promising components for wood preservation. In this work, the main approach was to split condensed tannins into smaller fractions by chemical hydrolysis and evaluate their suitability for beech wood impregnation. Commercial extract from black wattle was treated with mineral acid of low concentration. The volatile hydrochloric acid was completely removed after reaction by evaporation in the course of freeze-drying. The modified extract was then applied as aqueous solution into beech wood. The water resistance of the modified beech wood was not increased significantly, and scanning electron microscopy (SEM) showed no evidence of tannin successful bonding within wood cells. Nevertheless, after strong leaching cycles, part of the extract accumulated in fibers. Moreover, lyophilization was found to be a suitable technique to eliminate volatile acids from temperature-sensitive extracts, such as tannins. These findings could help in the development of water-borne tannin formulations for wood protection, while using phlobaphene formation as a potential natural pathway of tannin autocondensation.

Study of the kinetics of calcium molybdate leaching with sodium carbonate solutions

Calcium molybdate forms powellite, it is produced as a result of oxidizing roasting of off-grade molybdenum sulphide concentrates and other molybdenum materials with calcium additives (calcium oxides and hydro xides, calcium chlorides) in air at the temperatures of 550–600 oC. Use of Na2CO3 solutions enables an efficient recovery of Мо from CaMoO4 and a quantitative removal of impurities. To determine the optimum conditions for this process, one would need data on CaMoO4 leaching within a broad range of Na2CO3 concentrations and at high temperature and one would need to analyze the composition of the solid phase and the kinetic parameters of the process, i.e. rate and rate-controlling step. The authors look at the CaMoO4 leaching kinetics in 1.0–2.5 mol/l Na2CO3 solutions at 60–90 oC. It was found that the process rate is dictated by the stirring intensity and tends to increase with a rising temperature and the reagent concentration rising in the range of 1.0–1.5 mol/l. A higher concentration of Na2CO3 has no effect on the reaction rate. An apparent reaction order was determined in the Na2CO3 concentration range of 1.0–1.5 mol/l. An equation is proposed for calculating the CaMoO4 dissolution rate for the Na2CO3 solution and the temperature of 80 oC. It was established that a kinetic mode of leaching takes place in the soda concentration range of 1.0–1.5 mol/l amid intensive stirring. It is demonstrated that, within the studied Na2CO3 concentration range, calcite СаСО3 is formed after vaterite, a less stable phase of calcite, with crystallization of double sodium-calcium carbonates Na2Са(CO3)2·nH2O (n = 0, 2, 5) occurring at the same time. With the concentration of soda being >1.5 mol/l, the process is controlled by internal diffusion. In this region, the leaching rate is independent of the Na2CO3 concentration. Formation of double carbonates is associated with an additional consumption of soda. Therefore, when using this system one should consider how CaMoO4 typically dissolves in Na2CO3 solutions. The presence of these compounds in the soda solution after molybdenum leaching may impact the recovery of Мо from the solution using the known techniques. It may also hinder the recirculation of sodium carbonates going for the second leaching cycle.

Durability of sorption of per- and polyfluorinated alkyl substances in soils immobilised using common adsorbents: 1. Effects of perturbations in pH

The global problem of groundwater being contaminated with per- and polyfluoroalkyl substances (PFASs) originating from highly contaminated soils has created a need to remediate these locations. In situ immobilisation of PFASs in soil by applying sorbents is often a preferred low-cost technique to reduce their mobility and leaching to groundwater, but the long-term efficacy of sorbents has not yet been investigated. In this study, the longevity of remediation of two different soils by two common sorbents (RemBind®, and pulverized activated carbon, Filtrasorb™ 400) was assessed. Regulatory agencies often rely on standardised leaching procedures to assess the risk of contaminant mobility in soils. Hence, the Australian Standard Leaching Procedure and the U.S. EPA Leaching Environmental Assessment Framework were applied to quantify the desorption/leaching of a wide range of PFASs from unremediated and remediated soils under a range of pH conditions (pH 2 to 12). Ease of desorption and subsequent leaching from the unremediated soils was related to C-chain length; while short-chain PFASs were easily desorbed and leached, long-chain PFASs were more difficult to desorb. Desorption of long-chain PFASs was also pH dependent in unremediated soils, with desorption being greater at high pH. Both sorbents retained PFASs strongly in the remediated soils (> 99% for most PFASs) across a broad range of pH conditions, with only small differences between the sorbents in terms of efficacy. Both sorbents showed better retention of PFASs under low pH conditions. Remediation of PFAS-contaminated soils with these sorbents could be considered robust and durable in terms of changes in soil pH, with little risk of subsequent PFASs desorption under normal environmental pH conditions. Ultimately, to give regulators and site owners the greatest level of confidence that immobilisation is stable for the longer term, it should also be tested under repeated cycles of leaching and under different conditions.

Investigation on the quality of silicon extracted from the Padma river sand using magnesio-aluminothermic process

Investigation on the quality of the extracted Silicon (Si) from the sand of the Padma river of Bangladesh using the Magnesio-Aluminothermic process has been presented in this work. Magnesio-Aluminothermic process, which is low-energy, low-cost and CO2 free compared to conventional carbothermic process, was used for the extraction of Si from the sand. By performing the thermite process, Si was extracted as a eutectic mixture of Aluminium and Si, following that, several cycles of acid leaching were used to obtain highly pure polycrystalline silicon. After grinding the cleaned sand and making a homogeneous mixture with associated chemicals and ignition materials, modified Aluminothermic reaction was performed to produce a eutectic mixture of Si and Al. Grinded eutectic mixture of Si and Al was then purified with acid leaching and finally above 97% pure crystalline Si was extracted. XRD (X-ray diffraction) and Raman Spectroscopy confirmed the polycrystalline nature of Si where XRF (X-ray fluorescence) and EDX (Energy Dispersive X-ray Spectroscopy) corroborated the high purity of extracted Si describing the chemical composition.
 Bangladesh Journal of Physics, 26(2), 33-40, December 2019

Nutrient retention and release from raw exhausted grape marc biochars and an amended agricultural soil: Static and dynamic investigation

Biochar is the solid by-product of biomass thermochemical conversion via pyrolysis technique. Biochar addition to croplands as an organic amendment can improve soil properties and increase agricultural productivity. However, these positive effects depend largely on biomass feedstock and pyrolysis conditions. In this study, nutrient release from biochars derived from the slow pyrolysis of exhausted grape marc (EGM) at 300, 400 and 500 °C (EGM300, EGM400 and EGM500) was investigated through five successive leaching assays in batch mode for a total duration of 10 days. Then, nutrient leaching/retention kinetics of an agricultural soil amended with EGM500 (1% and 5% w/w) was assessed under dynamic conditions in columns. The batch experiments showed that with the exception of P, the nutrient release efficiency from the three biochars significantly increased with the increase of the number of leaching trials. The highest released amounts were observed at the fifth leaching cycle for K, Ca, P and Mg, which were about 45.5%, 41.5%, 229.5% and 48.9% higher than those registered during the first leaching assay. Regarding the column release experiments, a biochar content of 5% in the agricultural soil resulted in an increase of water leached NO3− and K+ by about 181.4% and 521.3%, respectively, and a significant reduction in Na+ and Ca2＋ transport as compared to unamended soil. In a second phase, outcomes of column feeding with a nutrient solution showed that PO43− and NO3− retention by biochar-amended soils is low. Thus, the use of EGM biochar as a slow release biofertilizer could be considered as a promising agricultural practice and a sustainable solution for biowaste management.

Pb-Based Perovskite Solar Cells and the Underlying Pollution behind Clean Energy: Dynamic Leaching of Toxic Substances from Discarded Perovskite Solar Cells.

Toxicants like Pb in lead-based perovskite solar cells (PSCs) may become available to humans through leaching and transport through water, air, and soil. Here, we summarize the potential toxicity of different substances in PSCs and determine the leaching concentration of typical heavy metals used in PSCs through dynamic leaching tests (DLTs). Extraction fluids for the standard toxicity characteristic leaching procedure, synthetic precipitation leaching procedure, and deionized water were used as the DLT leaching solutions. Results indicated that the leaching concentration of Pb exceeded the hazardous waste limit of 5 mg/L. In addition, Pb was found to continuously leach out in the leaching cycles of water extraction. The findings confirmed that discarded PSCs may release Pb when subjected to water, rain, and landfill leachate. Total organic carbon and chemical oxygen demand analyses indicated that discarded PSCs could increase the oxygen consumption and may release CO2 into the environment.

Microplastics release precursors of chlorinated and brominated disinfection byproducts in water

Microplastics (MPs) are prevalent global pollutants that are being detected in aquatic ecosystems and drinking water sources around the world. In addition to plastic polymers, MPs contain various chemical substances (known as “additives”) that can leach and risk water quality. In this paper, we investigated for the first time the potential release of disinfection byproducts (DBPs) precursors when MPs are exposed to hydrolysis and/or degradation by simulated sunlight. Seventeen MPs with seven different polymer types were collected either as commercial products (e.g. drinking water bottles, shopping bags, recycled plastics, etc.) or pure/virgin polymers. Results showed high release of dissolved organic carbon (DOC) from five MP samples and a significant increase in bromide concentrations from four MPs. DBPs formation potential (DBPFP) experiments with MPs’ leachates showed higher concentrations of chlorinated trihalomethanes (THMs), haloacetonitriles (HANs), and total organic halogens (TOX) in three samples, while a significant shift to brominated DBPs was observed in samples containing bromide. Extending the leaching experiments to four consecutive cycles showed that the leaching of DOC and DBPs’ precursor significantly decreased after the second leaching cycle. Further analysis revealed that the reactivity of the leached DOC – indicated by THMFP yields – was comparable to those of several raw waters that supply drinking water treatment plants. The leached THMs and TOX from MPs that were exposed to UVA irradiation were in general higher than MPs that were run under dark conditions.

Feasibility of Manufacturing Strand-Based Wood Composite Treated with β-Cyclodextrin-Boric Acid for Fungal Decay Resistance.

The feasibility of using β-cyclodextrin (βCD) as an eco-friendly carrier of boric acid for the protection of strand-based wood composites against decay fungi was evaluated. The formation of a βCD–boric acid (βCD–B) complex was confirmed by the appearance of the boron–oxygen bond by using attenuated total reflection–Fourier transform infrared spectroscopy. Chemical shifts of around 6.25 and 1.41 ppm were also observed in 1H Nuclear Magnetic Resonance (NMR) and 11B NMR spectra, respectively. The βCD–B preservatives at two levels (5 and 10 wt.%) were uniformly blended with southern pine strands that were subsequently sprayed with polymeric methylene diphenyl diisocyanate (pMDI) resin. The blended strands were formed into a loose mat by hand and consolidated into 25 × 254 × 12 mm oriented strand boards (OSB) using a hot-press. The OSB panels were cut to end-matched internal bonding (IB) strength and fungal decay resistance test specimens. The vertical density profiles (VDPs) of the IB specimens were measured using an X-ray based density profiler and the specimens with statistically similar VDPs were selected for the IB and decay tests. The IB strength of the treated specimens was lower than the control specimens but they were above the required IB strength of heavy-duty load-bearing boards for use in humid conditions, specified in the BS EN 300:2006 standard. The reduced IB of preservative-treated OSB boards could be explained by the destabilized resin upon the addition of the βCD–B complex, as indicated by the differential scanning calorimetry (DSC) results. The resistance of the OSB panels against two brown-rot fungi (i.e., G. trabeum or P. placenta) was evaluated before and after accelerated leaching cycles. The treated OSBs exposed to the fungi showed an average mass loss of lower than 3% before leaching, while the untreated OSBs had 49 and 35% mass losses due to decay by G. trabeum or P. placenta, respectively. However, upon the leaching, the treatment provided protection only against G. trabeum to a certain degree (average mass loss of 15%). The experimental results suggest that protection efficacy against decay fungi after leaching, as well as the adhesion of the OSB strands, can be improved by increasing the amount of pMDI resin.

Effect of modified basic oxygen furnace slag on the controlled release of nitrate nitrogen and the functional microbial community in soil

The specific surface area and active adsorption sites of basic oxygen furnace (BOF) slag increase after BOF modification. The addition of modified BOF slag to the soil may enable the control of nitrate nitrogen (NO3–N) leaching and also affect the functional microflora in the soil. In this study, soil column leaching experiments were conducted to explore the effects of adding modified slag to the soil on the controlled release of NO3–N and the main functional microbial communities involved in nitrification and denitrification processes. The experimental design included seven column groups: a soil control group (CT); soil groups with 2.5%, 5%, and 10% raw slag (S1, S2, S3); and soil groups with 2.5%, 5%, and 10% modified slag (MS1, MS2, MS3) that were subjected to three cycles of leaching, each of which were comprised of five leaching treatments. After the three cycles of leaching, significantly less NO3–N had leached from the modified slag group compared to the CT and the raw slag groups (P < 0.05). Although both slag treatments increased soil pH and decreased the oxidation reduction potential of the soil leaching solution, the addition of modified slag had less effect on soil pH than the addition of raw slag. During column leaching, the group with modified slag had a higher gene abundance of functional microflora compared with the group with raw slag. Similarly, the modified slag group had a higher diversity and richness of denitrifying bacteria, ammonia-oxidizing archaea, and ammonia-oxidizing bacteria than the raw slag group. In conclusion, the addition of modified slag to soil effectively decreased the NO3–N leaching and had relatively little effect on the functional microbial community in the soil.

Effect of Multiple Leaching Cycles on Decay Resistance of Micronized Copper Azole–Treated Southern Pine Sapwood

Abstract Copper remains one of the key biocides for protecting timber in soil contact. Historically, copper-based preservatives relied on solubilized copper. Over the past decade, micronized copper systems have largely replaced soluble copper systems in this application. While micronized copper chemistries have been shown to perform well over time with reduced copper leaching compared to solubilized copper, data are lacking on the effects of repeated leaching cycles on resistance of the timber to fungal attack. The potential effects of repeated leaching cycles of micronized copper azole–treated southern pine (Pinus spp.) blocks on both copper losses and resistance to fungal attack were explored over 20 leaching cycles using Gloeophyllum trabeum and Rhodonia placenta as test fungi. Copper losses during leaching were elevated for the first two cycles and steadily declined with additional cycling. There were no noticeable differences in fungal-associated weight losses in blocks exposed to G. trabeum. There was only a slight increase in average block weight losses with R. placenta, although blocks exposed to this fungus experienced higher weight losses with increased leaching cycles. The results suggest that repeated leaching exposures may produce some localized increases in susceptibility to fungal attack, but the overall effects were minor.

Nutrient release from K-feldspar ore altered in hydrothermal conditions

The development of potash materials from local K-bearing resources such as aluminosilicate minerals is desirable to overcome reliance on imported fertilizers in tropical countries. However, the nutrient release from such materials follows a time-dependent profile that is not well-understood and that is significantly different if probed at agronomic or geological timescales. This work investigates the nutrient release from a calcium–aluminum–silicate-hydrate (C–A–S–H) material obtained via hydrothermal alteration of K-feldspar ore and CaO. The C–A–S–H hydrothermal material is subjected to sequential leaching cycles with diluted HNO3 (initial pH = 5), renewing the leaching solution at every cycle. X-Ray Powder Diffraction (XRD) is used to monitor changes in the material mineralogy as the leaching progresses, showing a relative increase of calcite (up to 7 wt%) and amorphous phase (up to 23 wt%). Inductively Coupled Plasma Mass Spectrometry (ICP-MS) of the leachates is used to monitor the release of K, Ca, Si and Al, and shows that the material releases K nutrient at every leaching cycle. The pH of the leachates shows that as the content of calcite in the material increases a buffering capacity at pH ≈ 9.6 is developed by the material. The mineralogy, nutrient release, and pH results presented in this study suggest a potential application of the material as a slow release fertilizer when compared to KCl. Experimental results also imply that kinetic parameters rather than solubility are more suited to describe the fertilizer value of silicate materials.

Ferric Leaching of Low-Grade Zinc Concentrate with a Biologically Produced Solution

The process of ferric leaching of a zinc concentrate (43.3% zinc, 2.03% copper, and 13.6% iron) with a biologically produced solution has been studied. Conditions that can increase its efficiency have been found. The extraction of copper and zinc was found to increase with an increase in temperature from 25 to 80°C. The effect of pH on this process was studied, and the extraction of metals was found to decrease with a decrease in pH from 1.3 to 0.7. It was determined that the Fe3+ concentration in the leaching solution did not affect copper recovery, while zinc recovery increased with an increase in the oxidant concentration. At a solid content in the suspension of 1%, the specific zinc leaching rate was 0.86 g/(g h), and for copper this rate was 0.46 g/(g h). These values decreased to 0.54 and 0.36 g/(g h), respectively, with an increase in pulp density of up to 10%. Thus, the parameters for effective concentrate leaching were found: a temperature of 80°C, a pH of 1.3, a solid content in the suspension equal to 10%, and an initial Fe3+ concentration of 25.0 g/L. Under these conditions, four cycles of ferric leaching of the concentrate were carried out, as a result of which 92.3% of zinc and 51.6% of copper were extracted into the solution. The contents of zinc and copper in the solids decreased to 6.17 and 1.82%, respectively.