This study aimed to evaluate the effect of modified nanoscale zero-valent iron (SAS-nZVI) on chemical leaching of lead and cadmium composite contaminated soil by citric acid (CA). The synthesized SAS-nZVI was used as a leaching aid to improve the removal rate of soil heavy metals (HMs) by CA chemical leaching. The effects of various factors such as SAS-nZVI dosage, elution temperature and elution time were studied. At the same time, the effect of chemical leaching on the basic physical and chemical properties of soil and the morphology of HMs was evaluated. The results show that when the SAS-nZVI dosage is 2.0 g/L, the leaching temperature is 25 °C, and the leaching time is 720 min, the maximum removal rates of Pb and Cd in the soil are 77.64% and 97.15% respectively. The experimental results were evaluated using elution and desorption kinetic models (Elovich model, double constant model, diffusion model). The elution and desorption process of Pb and Cd in soil by SAS-nZVI-CA fitted well with the double-constant model, indicating that the desorption kinetic process of Pb and Cd is a heterogeneous diffusion process, and the elution process is controlled by diffusion factors. After leaching with SAS-nZVI-CA, the physical and chemical properties of the soil changed little, the mobility and toxicity of HMs in the soil were reduced, and the HMs content in the leaching waste liquid was reduced. It can be concluded that SAS-nZVI enhances the efficiency of CA in extracting Pb and Cd from soil, minimizes soil damage resulting from chemical leaching technology, and alleviates the challenges associated with treating leaching waste liquid.

The flourishing expansion of the lithium-ion batteries (LIBs) market has led to a surge in the demand for lithium resources. Developing efficient recycling technologies for imminent large-scale retired LIBs can significantly facilitate the sustainable utilization of lithium resources. Here, we successfully extract active lithium from spent LIBs through a simple, efficient, and low-energy-consumption chemical leaching process at room temperature, using a solution comprised of polycyclic aromatic hydrocarbons and ether solvents. The mechanism of lithium extraction is elucidated by clarifying the relationship between the redox potential and extraction efficiency. More importantly, the reclaimed active lithium is directly employed to fabricate LiFePO4 cathode with performance comparable to commercial materials. When implemented in 56 Ah prismatic cells, the cells deliver stable cycling properties with a capacity retention of ∼90% after 1200 cycles. Compared with the other strategies, this technical approach shows superior economic benefits and practical promise. It is anticipated that this method may redefine the recycling paradigm for retired LIBs and drive the sustainable development of industries.

Polybrominated diphenyl ethers are persistent disrupters assimilated by organisms, yet little is known about their link to plastic ingestion and health effects. In an experiment, two groups of yellow-legged/lesser black-backed gulls (Larus michahellis/Larus fuscus) were fed plastics with BDE99 to assess leaching into brain, preen oil, liver and fat tissues and evaluate effects on health and stress parameters. Although most plastic was regurgitated, we observed a clear relation between plastic ingestion and chemical leaching. BDE99 exhibited higher levels in brain tissue of gulls from the plastic groups. Also, only values of cholinesterases measured in plasma were significantly reduced in the \'plastic\' groups. Cholinesterase activity in the brain also tended to decrease, suggesting a negative effect in gulls\' neurofunction. Results indicate that chemical leaching occurs, even when plastics stay in the stomach for a short period of time and showed that this can affect gulls\' health.

In this study, chemical leaching and electrokinetic technology were used to remediate heavy metal contaminated soil to elucidate its effectiveness and mechanisms. Chemical leaching agents of FeCl3, Fe(NO3)3, KCl, KNO3, and HCl solutions were selected, and the effects of Fe3+, K+, H+, and Cl- on four heavy metal (Cd, Pb, Cu, and Zn) removals were compared and analyzed. Then, the influence of the speciation of heavy metals in soil after chemical leaching on the electrokinetic remediation efficiency was studied. The results showed that Fe3+, K+, H+, and Cl- had different effects on the four heavy metal removals; for Cd and Zn, the removal effect of H+was the most effective, but for Pb and Cu, the effect of Fe3+ was the most obvious. On the whole, FeCl3 and Fe(NO3)3 showed the best removal effect for Cd, Pb, and Cu. For the removal of Zn from the soil, the difference in the removal effect of the five leaching agents was not obvious. In comparison with that of FeCl3 and Fe(NO3)3, the HCl solution had a moderate removal effect on the four heavy metals in the soil, and the neutral salts KCl and KNO3 had little removal effect on the four heavy metals. Especially for Cd and Cu, KCl and KNO3 addition significantly increased the removal of heavy metals through the subsequent electrokinetic remediation. After the chemical leaching, electrokinetic remediation could make heavy metals in the topsoil (0-10 cm) migrate downward and enrich the 10-20 cm and 20-30 cm soil layers, which requires further studies to resolve.

Electronic waste generation is indeed a global concern; therefore, appropriate management and recycling are becoming highly significant. Printed circuit boards (PCBs) are significant portion of e-waste; contains a large number of valuable metals, rendering this material an important recovery resource. Among all other metals, the high Copper concentration of PCB residues, which is often ten times higher than that of rich-content rocks, makes these residues an appealing secondary source of Cu recovery. The primary goal of this study is to develop a simple and economical method for recovering Cu from waste PCBs. To leach metals, a combination of citric acid, acetic acid, and hydrogen peroxide (H2O2) was utilized. The influence of systemic factors such as citric acid concentration, acetic acid concentration, and H2O2 concentration on Cu leaching process was investigated. The results proved that the combination of citric acid, acetic acid, and H2O2 has increased the leaching efficiency of copper. More copper was dissolved when leaching with 0.5-1.5 M citric acid, 2.5-7.5%, and 2.5-7.5% H2O2 at 30 °C; however the individual acids produces less amount of Cu such as 26.86 ppm, 22.33 ppm, and 6.28 ppm whereas, high amount of Cu is obtained from the leaching solution containing 1 M citric acid, 5% acetic acid and 5% H2O2 with 325.89 ppm respectively. Thus, the combination of these acids and can be used as standardized method for leaching of Cu. These findings suggest that organic acids can replace inorganic acids as eco-friendly lixiviants for waste management.

The ever-increasing demand for ferrochrome alloys has resulted in a substantial accumulation of ferrochrome slag by-products in many mining areas. On the other hand, the ferrochrome slag has been identified as one waste material that is rich in magnesium (Mg) and has not been effectively exploited. Beneficiating of ferrochrome slag (FCS) waste material is envisaged as a means of achieving sustainable recovery of Mg. Previous studies have used sulphuric acid as a lixiviant for leaching FCS at moderate temperatures to recover Mg. In this study, the recovery of Mg from ferrochrome slag was investigated using hydrochloric acid (HCl) as the lixiviant at low temperatures. Previous studies have shown that various metal oxides have been proven to be more amenable to leaching using HCl. This study examined the effects of acid content, leaching temperature, and reaction time on the recovery of Mg from FCS. Kinetic and thermodynamic analysis of the leaching process were also investigated as these are critical factors for maximum extraction of the Mg. The results showed that the highest recovery of Mg of 88.2% was obtained from FCS using 5 M HCl with a solid to liquid ratio of 1:10, mixing intensity of 250 rpm, reaction time and temperature of 150 min and 70 °C, respectively. The shrinking core model (SCM) was used in kinetic analysis to find the experimental data\'s best fit. A linear relationship was obtained with the coefficient of determination for the chemical reaction model (Kc) of >0.9 which indicates a good fit. The activation energy obtained for the diffusion and chemical reaction models were 95.44 and 41.45 kJ/mol, respectively, demonstrating that the rate-limiting phase is the one involving the chemical reaction.

Physical friction between a tire and the road surface generates tire wear particles (TWPs), which are a source of microplastics and particulate matter. This study investigated the trends of chemical leaching from TWPs depending on the treadwear rating of the tire. A road simulator was used to produce TWPs from tires with various treadwear ratings. Liquid chromatography-tandem mass spectrometry was used to analyze the chemical leaching from TWPs, with a particular focus on benzothiazole and its derivative 2-hydroxy benzothiazole. However, chemical mapping via high-resolution tandem mass spectrometry detected another derivative: 2-mercaptobenzothiazole. The benzothiazole groups were observed to have different leaching tendencies, implying that using benzothiazole as a marker compound may lead to incorrect TWP quantitation. The results of this research also suggest that the ecotoxicological influence of TWPs can vary with the treadwear rating of a tire.

The heavy metals (HMs) contained in sewage sludge are some of the largest obstacles that hamper the usage of sewage sludge in land application (e.g. fertilizer, soil improver). The conventional chelators, e.g., ethylenediaminetetraacetic acid (EDTA), were effective in the remediation of HMs polluted sewage sludge, but suffered from an evident drawback of low biodegradability. Therefore, the applicability of a new biodegradable chelator, methyl glycine diacetic acid (MGDA), to extract HMs from sewage sludge was carried out and compared with EDTA. The experimental parameters affecting the performance of MGDA were optimized. Leaching results showed that in general, MGDA exhibited higher Zn leaching efficiency and similar Cu, Ni and Cr leaching efficiencies with EDTA at same pH and dosage conditions. The maximum Zn, Cu, Ni and Cr leaching efficiencies of MGDA were 94.1% ± 4.5%, 58.2% ± 3.1%, 78.2% ± 2.3% and 54.6% ± 2.5%, respectively. The leaching efficiency plateaued within a reaction time of 4 h, but that of Cu and Ni showed a slightly decreasing trend during hours 4 to 10. In raw sewage sludge, the Zn and Cu were mainly presented in the organically bound fraction, i.e., 45.3 ± 3.2% of total Zn and 48.3 ± 1.4% of total Cu. The addition of MGDA and EDTA caused obvious distribution transformations in Zn and Cu from the organically bound fraction to soluble fraction. According to the reduced partition index calculation, the mobility of Zn, Cu, Ni, and Cr was not significantly lowered after the MGDA treatment. However, the HMs secondary pollution risk of the sludge was reduced due to the drop of the total HMs content after chelator leaching. Findings from this study suggest that MGDA could be a potential environment-friendly alternative for refractory chelators (e.g. EDTA) in the decontamination of HMs from sludge.

This review is intent on the environmental pollution generated from printed circuit boards and the methods employed to retrieve valuable and hazardous metals present in the e-wastes. Printed circuit boards are the key components in the electronic devices and considered as huge e-pollutants in polluting our surroundings and the environment as a whole. Composing of toxic heavy metals, it causes serious health effects to the plants, animals and humans in the environment. A number of chemical, biological and physical approaches were carried out to recover the precious metals and to remove the hazardous metals from the environment. Chemical leaching is one of the conventional PCBs recycling methods which was carried out by using different organic solvents and chemicals. Need of high cost for execution, generation of secondary wastes in the conventional methods, forces to discover the advanced recycling methods such as hydrometallurgical, bio-metallurgical and bioleaching processes to retrieve the valuable metals generate through e-wastes. Among them, bioleaching process gain extra priority due to its higher efficiency of metal recovery from printed circuit boards. There are different classes of microorganisms have been utilized for precious metal recovery from the PCBs through bioleaching process such as chemolithoautotrophy, heterotrophy and different fungal species including Aspergillus sp. and Penicillium sp. The current status and scope for further studies in printed circuit boards recycling are discussed in this review.

Hexavalent chromium [Cr(VI)] has strong mobility and it can enter into deep regions of soil. Cr(VI)-contaminated soil remediation is the process of removing Cr(VI) present in deep soils and any residual Cr(VI). In this study, the Cr(VI)-contaminated soil in Chongqing was investigated, and the remediation and economic feasibility of chemical leaching and reduction combined with a soil repairing approach was explored. The results showed that the leaching reagent, liquid-solid ratio, leaching time, reduction agent dosage, reduction temperature and reduction time had significant (P < 0.05) effects on the remediation of Cr(VI). At 0.02 mol/L oxalic acid and citric acid using a liquid-solid ratio of 5:1 and leaching time of 45 min, the removal rate of Cr(VI) was 62.7%, the residual Cr(VI) in soil was 126 mg/kg, and the soil pH was 4.09 after leaching. Between 25 and 90 °C, and at a molar ratio of 25:1 of FeSO4•7 H2O to Cr(VI), the reduction rate of Cr(VI) in soil after reduction was 54.0-98.4%, and the leaching concentration of Cr(VI) in soil was 0.01-0.29 mg/L. The optimal reduction was at 90 °C for 60 min, resulting in only 2.7 mg/kg of residual Cr(VI) in soil. The cost of this technology to treat the area studied was 826 ¥/ton of soil, which represents an economically feasible method for Cr(VI)-contaminated soil remediation.