Corn processing waste represents an abundant, renewable, and low-cost lignocellulosic resource with considerable potential for environmental remediation applications. Large quantities of residues generated during corn processing, including cobs, husks, bran, and other by-products, are produced annually and can be utilized directly as native biomass or converted through thermochemical processes into hydrochars and biochars. This systematic review provides a comparative analysis of native corn processing biomass, hydrochars produced via hydrothermal carbonization, and biochars obtained through pyrolysis, with a focus on their potential as adsorbents for the removal of organic and inorganic pollutants from soil and water systems. Particular attention is given to the influence of thermochemical conversion processes on the physicochemical properties of the materials, including surface chemistry, porosity, functional groups, and structural characteristics, which govern adsorption mechanisms such as ion exchange, electrostatic interactions, surface complexation, hydrogen bonding, and π–π interactions. Furthermore, the advantages and limitations of each material type are discussed, together with key environmental and techno-economic considerations related to their production and practical application, including indicative production costs (USD per kg of adsorbent) and cost–performance relationships in terms of adsorption capacity. By linking biomass conversion processes, material properties, and adsorption performance, this review aims to provide a comprehensive overview of corn processing waste valorization and to support the development of sustainable adsorbent materials for soil and water remediation. A total of 36 studies were included in the qualitative synthesis following PRISMA guidelines.

Efficient extraction of zinc from polymetallic concentrates is crucial for the metallurgical industry. Traditional leaching techniques often rely on strong oxidizing agents, which can be wasteful and environmentally harmful. While cyclic oxidation systems like the Fe³⁺/Fe²⁺ pair are known, they often fail to achieve high leaching rates, especially when the raw material contains multiple sulfide minerals. In this study, we developed a novel oxidation system using manganese dioxide (MnO₂) as the primary oxidizing agent and potassium iodide (KI) as a supporting material to create an I₂/I⁻ oxidation cycle in a sulfuric acid medium, at an atmospheric pressure between 40 °C and 80 °C. Leaching experiments were conducted under varying temperatures and KI doses. The results demonstrated that for the MnO₂-KI system, a zinc leaching degree of 89.78% was achieved after 3 h of leaching at 80 °C, and kinetic studies indicated that the leaching process is diffusion-controlled (through the thin film), with an activation energy of 27.65 kJ mol⁻¹. Moreover, this system offers an improved method for separating iodine from the leachate upon completion, enhancing the overall process efficiency. It also opens opportunities to test other primary oxidizing agents in combination with iodide salts. These findings suggest that the MnO₂-KI oxidation system offers a promising approach for improving zinc recovery from sphalerite concentrates.

Hydrothermal carbonization (HTC) produces biomass-derived hydrochar, a promising adsorbent for environmental remediation. Lignocellulosic biomass serves as the primary feedstock, and adsorption performance depends on biomass structure and HTC conditions, especially carbonization temperature. This review highlights hydrochar’s adsorption capabilities and modification strategies, including physical treatments to increase surface area and chemical treatments to introduce oxygen-containing functional groups. Heteroatom doping and acid-base modifications notably enhance the removal of metal ions and dyes. Hydrothermal treatment is key to producing tailored hydrochars for specific applications. Future research should focus on combining physico-chemical modifications, deepening understanding of adsorption mechanisms, and broadening hydrochar applications. These efforts will advance the use of biomass hydrochars as effective, sustainable adsorbents for pollution control while addressing waste management.

This study examined the leaching behavior of copper and iron from a sphalerite concentrate in sulfuric acid utilizing an ensemble MnO₂–KI oxidizing system. The temperature was shown to significantly influence the leaching kinetics, with the efficiency notably improving between 40 °C and 80 °C. The introduction of KI affected the balance between sulfur passivation and oxidant availability, facilitating increased leaching efficiencies. At 3 wt% KI, maximum recoveries of 82.1% Cu and 85.3% Fe were achieved, which indicates a notable decrease in surface passivation. Kinetic study analysis revealed low activation energies of 28.90 kJ mol⁻¹ for copper and 18.94 kJ mol⁻¹ for iron, indicating that both processes proceed readily at moderate temperature regimes. Despite being diffusion-controlled, the mechanisms of dissolution are different: iron leaching is more complicated, involving pyrite oxidation, sulfur layer formation, transformation to marcasite, and ultimately iron (III) release, whereas copper leaching involves direct interaction of chalcopyrite with the oxidants, similar to the behavior of sphalerite.

Waste products of zinc hydrometallurgy, such as Pb–Ag jarosite sludge, represent a significant environmental problem due to toxic properties associated with elevated lead content. At the same time, this material has economic value, making its valorization beneficial from both ecological and financial perspectives. This study investigates the chloride leaching of pretreated Pb–Ag jarosite sludge, which underwent sulphation roasting followed by water leaching. The experiments were conducted with a constant solid/liquid ratio of 1:20, a stirring rate of 150 rpm, and using a 4 mol dm³ MgCl₂ solution as the leaching agent, while temperature (40–80 °C) and leaching time (up to 120 min) were varied. The results showed that temperature significantly affects the lead leaching degree, with the highest (95%) achieved at 80 °C after 60 min. Kinetic analysis revealed a diffusion-controlled mechanism, with an activation energy of 18.40 kJ mol⁻¹. Due to the characteristics of the leaching curve, the process was divided into four segments, with corresponding activation energies determined for each segment (16.48, 11.80, 13.88, and 20.50 kJ mol⁻¹). The proposed MgCl₂ system enables efficient lead leaching with a reduced amount of leaching agent, thus representing a more sustainable approach to the valorization of Pb–Ag jarosite sludge.

Understanding the dissolution kinetics of phosphate glasses is essential for designing materials with tailored durability, optimizing their performance across various applications, and minimizing their environmental impact. The hydrolysis of phosphate glass refers to its degradation in the presence of water, where phosphate bonds break, leading to the gradual dissolution of the glass network. This process is influenced by factors such as composition, pH, temperature, and the presence of ions within the glass matrix. This study investigates the hydrolysis kinetics of polyphosphate glass in deionized water and a 2% citric acid solution, focusing on how solvent properties affect the dissolution process. Experimental results indicate that ion release rates range from 8.74 × 10⁻⁴ to 5.44 × 10⁻² g·m⁻²·h⁻¹ in deionized water, while in a 2% citric acid solution, they vary from 9.44 × 10⁻³ to 6.92 × 10⁻² g·m⁻²·h⁻¹. The activation energies for ion release during hydrolysis are 41.5 to 65.2 kJ·mol⁻¹ in deionized water and 49.1 to 85.3 kJ·mol⁻¹ in the citric acid solution. Additionally, this paper presents the results of EDS analyses of the surfaces of compact polyphosphate glass samples after dissolution in both solvents, providing further insight into the material’s degradation behavior.