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A study involving the leaching of Cu and Co from a Cusingle bondCo ore in sulfuric acid (H2SO4), citric acid (CA) and oxalic acid (OA) using hydrogen peroxide (H2O2) as oxidant, was carried out. The ore was characterised by x-ray fluorescence (XRF), x-ray diffraction (XRD) and scanning electron microscopy coupled with energy-dispersive x-ray spectroscopy (SEM-EDX). The results obtained indicate that increasing the time, temperature, and concentration of the leaching agent/oxidant enhanced the leaching efficiencies of Cu and Co, while a reduction in particle size (large surface area) favours the leaching of Cu and Co. The highest leaching efficiencies of 99.2 % and 94.0 % were obtained for Cu and Co, respectively, in a leaching system constituted by 1.0 M H2SO4 and 3.0 M H2O2 within 4 h at 65 °C. In contrast, the 0.8 M OA leaching system demonstrated a 97.1 % efficiency for Cu and 100.0 % efficiency for Co. The estimated activation energy in the temperature range of 25–65 °C is 40.7 kJmol−1 for Cu, while that of Co is 64.0 kJmol−1, which implies that the leaching is controlled by a surface chemical reaction. A comprehensive analysis demonstrated that the reaction mechanism for Cu leaching is diffusion-controlled at lower temperatures (<35 °C) and surface chemical reaction-controlled at temperatures higher than 35 °C.

Mining industries have long relied on cyanidation as the primary method for gold extraction, but this process generates thiocyanates as a problematic byproduct, posing challenges for wastewater treatment and recycling. The stability of thiocyanates makes their reduction or elimination in mining wastewater difficult. In this study, a p-n heterojunction of ZnO and BiOI was created and evaluated for its ability to photodegrade thiocyanate ions under simulated solar conditions. Various analytical techniques revealed a highly porous structure with a sponge-like morphology and agglomeration in the synthesized heterojunction. The compound exhibited crystalline patterns without impurity peaks, a slight red shift in absorbance, and Type IV isotherm adsorption. The synthesized heterostructure achieved the complete destruction of thiocyanate ions in less than 30 min. The investigation of different process parameters indicated that the destruction of the contaminant by the heterostructure was influenced by the initial thiocyanate concentration, which decreased as the thiocyanate concentration increased. The peak photodestruction reaction was observed at pH 7. By applying a pseudo-first-order kinetic model, it was found that increasing the catalyst mass to 15 mg raised the rate constant from 0.188 to 0.420 min−1, while increasing the pH to 10 led to a 3.5-fold reduction. The strong correlation between the observed data and the predicted values of the pseudo-first-order kinetic model was indicated by the observed (R2) values. The findings of this study hold potential significance for mining industries, as it offers a potential solution for eliminating cyanide and thiocyanates from mining wastewater. The elimination of thiocyanate generation in the cyanidation process is crucial for mining companies, making this study valuable for the industry.

The improper disposal of discarded electronic and electrical equipment raises environmental and health concerns, spanning air pollution to water and soil contamination, underscoring the imperative for responsible management practises. This review explores the complex composition of discarded printed circuit boards (DPCBs), crucial components in electronic devices. Comprising substrates, electronic elements and solder, DPCBs showcase a heterogeneous structure with metal (30.0–50.0%) and non-metal (50.0–70.0%) fractions. Notably abundant in precious metals such as Au, Ag, and Pd, DPCBs offer a compelling avenue for recycling initiatives. The inclusion of heavy metals and flame retardants adds complexity, necessitating environmentally sound disposal methods. Ongoing research on smart disassembly, utilising 3D image recognition technology, underscores the importance of accurate identification and positioning of electronic components (ECs). The targeted approach of smart disassembly, centred on valuable components, highlights its significance, albeit with challenges in equipment costs and capacity limitations. In mechanical disassembly, techniques such as grinding and heat application are employed to extract ECs, with innovations addressing gas emissions and damage induced by overheating. Chemical disassembly methods, encompassing epoxy resin delamination and tin removal, present promising recovery options, whilst the integration of chemical and electrochemical processes shows potential. Efficient sorting, encompassing both manual and automated methods, is imperative post-disassembly, with smart sorting technologies augmenting accuracy in the identification and categorisation of ECs. In addition, explorations into NH3/NH4+ solutions for selective metal recovery underscore challenges and stress the necessity for meticulous process optimisation in environmentally sustainable PCB recycling. Challenges and future perspectives have also been expounded.

As the volume of e-waste continues to rise, it is crucial to sustainably manage printed circuit boards (PCBs) and their valuable metal components. PCBs are ubiquitous in modern society, powering a variety of electronic devices. The metal resource crisis and the imperative for a low-carbon circular economy have accelerated the development of e-waste recycling technology. High-value discarded PCBs represent a vital component of e-waste. However, discarded PCBs are deemed hazardous to the ecosystem due to the presence of heavy metals and brominated organic polymers. Thus, recycling metals from discarded PCBs is not only a strategic necessity for fostering a green ecological civilisation but also a crucial guarantee for ensuring a safe supply of mineral resources. This comprehensive review gives the profound details of PCBs, and the performance of and advances in the latest chemical metal recovery methods. Reviewing the latest metal recovery processes, we explored the application of diverse leaching agents, including ionic liquids (ILs), deep eutectic solvents (DESs), organic acids and amino acids. These solvents were assessed in terms of their recovery efficiencies, and most of them demonstrated excellent leaching performance. The role of optimising leaching parameters such as concentration, oxidants, pH, particle size, solid-to-liquid ratios (S/L), temperature, and contact time is underscored, offering insights into achieving sustainable PCB recycling practices. Most of these recent leaching methods successfully extracted base metals (Cu, Fe, Zn, Sn, etc.), as well as precious metals (Au and Ag), achieving leaching efficiencies exceeding 90.0%. Interestingly, their effectiveness can compete with that of traditional hydrometallurgical methods.

The aim of the study was to investigate the application of photocatalytic advanced oxidation (PAO) for the treatment of water contaminated with dark humic material from fynbos biome plants, which cannot be treated by conventional methods. The study used a fynbos species (Aspalathus linearis) to create a model wastewater that was compared with a brew made from black tea (Camellia sinensis). Two photocatalysts (TiO2 and ZnO) and three light sources (natural, halogen light, and UV light) were tested, with and without hydrogen peroxide. The treatment of the two teas by only photolysis was observed to be minimal. The study found that natural sunlight was not effective, but a combination of ZnO and halogen lamp exhibited the best performance, with a 60% degradation in 20 min under solar irradiation. The optimum catalyst concentration was identified as 10 g/L for both photocatalysts. The influence of some process parameters showed that a combination of an optimum dose of 5 mM H2O2 and solar radiation improved the performance of TiO2 from 16 to 47%. The photocatalytic reaction data were fitted to the pseudo first and second-order kinetic models in order to exploit the kinetic process of the photo-destruction reaction. The kinetic fits showed that the degradation reaction better adhered to the second-order kinetic model when only ZnO and solar radiation were applied, regardless of the tea type employed. The application of PAO in this novel and cost-effective way has potential for the abatement of contaminated water to potable water. The use of heterojunction photocatalysts could be explored in future research to further improve the process.

In this study, a variety of ZnO-based heterojunctions with disparate wt.% doping of WO3 and BiOI have been prepared for the photodestruction of methyl orange (MO) dye in aqueous solution. The composites were analysed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, optical studies, and nitrogen adsorption-desorption isotherms. The SEM images revealed non-uniform surfaces of the ZnO–BiOI based composites while mostly nodular morphology was observed for all three samples of ZnO-WO3. As the WO3 loading increased, more clustering was detected. The analysed samples exhibited characteristic peaks representative of the triclinic phase of WO3 and the hexagonal wurtzite structure of ZnO, while the diffractogram observed from the materials displayed distinct peaks corresponding to the crystalline phases of both BiOI and ZnO in their pure forms. Further evidence of the samples' characteristics includes the presence of distinct crystalline patterns without any impurity peaks, a red shift in the absorption spectra of the heterostructure, the detection of only the reference elements, and mostly Type IV isotherm adsorption. This study identified the ZnO-[10%]BiOI and ZnO-[10%]WO3 heterojunctions as the best performing photocatalysts, as MO was completely destroyed in 120 and 90 min, respectively. Thus, confirming 10% wt. as the optimal doping concentration for the best photo-activity in this study. The impact of varying process parameters demonstrates that at an elevated photocatalyst mass of 40 mg, both heterojunctions effectively degraded MO. The photodegradation efficiency of MO was more pronounced in strong acidic conditions (pH 2) when compared to high alkaline conditions (pH 11) for the ZnO-[10%]BiOI heterostructure. However, a decrease in performance was observed for both strong acidic and high alkaline pH values when the ZnO-[10%]WO3 heterostructure was applied. The kinetic analysis of the photodegradation study reveals that all the

Novel bio-based plasticisers for polyvinyl chloride (PVC) are a significant and growing area of interest. These compounds aim to replace toxic and petrochemical additives in commonly used plastic products. Plasticisers can comprise as much as 50% of the total mass of the PVC product. Epoxidised soybean oil (ESBO) is a commercially available bio-based plasticiser that is typically used at lower levels than traditional phthalates in PVC compounds because it does not show equivalent performance to existing phthalate plasticisers. Four derivatives of ESBO have been synthesised through reaction at the epoxide rings. These compounds have been evaluated in PVC formulations and compared to current petrochemical plasticisers, as well as ESBO. The product of methoxy polyethylene glycol and ESBO shows good plasticising ability, giving a PVC compound with higher tensile strength and elongation than dioctyl phthalate (DOP) and a lower glass transition temperature (Tg) than with the use of ESBO

A series of photocatalysts and heterojunction composites comprising ZnO, WO3, and BiOI with different loadings of WO3 and BiOI into ZnO was synthesized and applied for the destruction of 2-chlorobiphenyl (2CBP). The surface morphologies and elemental analysis of the as-synthesized composites were determined using a Carl Zeiss Sigma FE-SEM equipped with an Oxford X-act EDS; optical studies were conducted using a UV 1800 Shimadzu UV-vis spectrophotometer. The X-ray diffraction measurements were made with a Bruker D2 XRD instrument, while the BET surface area measurements, BJH pore size distribution, and isotherms were obtained using a Micrometrics TriStar 3000 instrument. The ZnO-[10%]BiOI heterostructure exhibited a superior photocatalytic activity in this study. The degradation reactions were fitted to the pseudo-first and second order kinetic models in order to exploit the kinetic process of the photodegradation reaction. The ZnO-[10%]BiOI hetero-photocatalyst showed the highest rate constants of 0.0054 min−1 and 0.0086 min−1 in both the first and second order kinetic models, respectively. When compared to undoped ZnO, the rate constant of the ZnO-[10%]BiOI heterostructure was observed to be nearly 5-fold higher, demonstrating the superior catalytic performance of the as-prepared ZnO-[10%]BiOI hetero-structured photocatalyst. All the photocatalysts and heterostructures showed increased rate constants in the second-order reaction kinetics model except for BiOI and ZnO-[5%]WO3, whose rate constants decreased from 0.0046 to 0.0041 min−1 and 0.0036 to 0.0029 min−1, respectively. The kinetic data show that it requires 128.4 min for the measured 2CBP concentration to be halved to the initial concentration when ZnO-[10%]BiOI is applied. A charge separation degradation mechanism is proposed to describe the process. The findings from this study suggest that ZnO-[10%]BiOI can potentially be used as an efficient and effective catalyst for the degradation of recalcitrant organ

Mild steel and various stainless steels are the workhorse alloys in construction and process industries, used in a myriad of applications. However, equally important are alloys and materials such as those of aluminium, magnesium, titanium, tantalum, zirconium and various combinations thereof with one another and other alloying additions. Equally varied are the corrosive environments in which these alloys and combinations are applied to limit degradation and supply solutions to their applications and maintenance. Despite this, corrosion remains a multibillion-dollar phenomenon worldwide.

Rotational molding (RM) is a useful process for making large hollow objects. Due to its relatively high toughness and forgiving thermal oxidative degradation behavior, polyethylene is a most widely used material. However, it has too low elastic modulus for some important applications which leads to adaptation of polypropylene (PP) as a RM material. PP requires specially tailored antioxidant (AO) packages if it is to have any chance of surviving the often long (up to ca. 30 minutes) cycle times associated with RM. During the study the addition of the following stabilizers and antioxidants (AO) to the PP copolymer were investigated: a hindered phenolic primary AO, a phosphite secondary AO, a thioester secondary AO and a hindered amine light stabilizer. Synergistic effects between the primary and secondary AOs, as well as optimum heating times, were investigated. During the investigation formulations were prepared by compression molding and bench-scale RM. The combination resulting in the most effective synergism is the hindered phenolic primary antioxidant combined with the phosphite secondary antioxidant. A gel silica controlled release agent for the stabilizers was also investigated but did not yield significant improvements in stabilization.