Heavy metal pollution in water resources, particularly cadmium and lead, poses a significant environmental and public health challenge, requiring the development of sustainable, efficient, and cost-effective water treatment methods. Therefore, this study investigates the biosorption capabilities of natural (SN) and surfactant-modified (SM) guava seed biosorbents to remove Cd and Pb from aqueous solutions. Guava seeds, an agricultural waste material, were treated with hexadecyltrimethylammonium bromide (HDTMA-Br) to enhance their adsorption efficiency. The biosorbents were characterized by FTIR, SEM-EDS, and zeta potential analysis to explain the surface modifications and their influence on the adsorption mechanisms. Batch experiments were performed to evaluate the effects of pH, contact time, temperature, biosorbent dosage, and concentration on Cd and Pb removal efficiencies. Adsorption isotherm and kinetic data were analyzed using mathematical models to obtain the basic parameters of the systems under study. The results showed that SM exhibited superior adsorption capacities of 328 mg/g for Cd and 594 mg/g for Pb at 25 °C, significantly outperforming SN. The study analyzed the thermodynamic parameters of adsorption systems, revealing endothermic and exothermic properties for SN and SM. Functional groups like hydroxyl and carbonyl were crucial for metal ion binding. HDTMA-Br introduced active sites and enhanced surface charge interactions. Regeneration tests showed reusability, maintaining over 85% efficiency after four cycles. Guava seeds could be cost-effective and sustainable biosorbents for heavy metal removal.

During grinding with forged steel media, sulphides such as pyrite undergo surface changes due to the occurrence of oxidation–reduction reactions, which affect its depression during the concentration process. For this reason, in this work, the surface modification of pyrite during grinding was studied; FTIR, ICP-OES, XRD and SEM-EDS were used for the materials’ characterisation. It was found that the pyrite obtained during grinding showed magnetic susceptibility due to the absorption and superficial formation of magnetite Fe₃O₄, Fe–O bonds identified by FTIR at 598 cm⁻¹, and of other species, such as oxy-hydroxy-sulphates at 696 cm⁻¹ and goethite α-FeOOH at 875 cm⁻¹. This caused the reversal of the zeta potential magnitude (ζ) from positive to negative at pH 8.3 and 30 min of grinding. The ζ of the pyrite throughout the studied pH ranges was, overall, positive, i.e., +5 mV. However, at pH 10.5 and 15 min of grinding, the ζ turned negative. This was associated with the formation of Fe–CO₃ (−2) bonds in the siderite, which were identified with the absorption bands corresponding to 756, 1448 and 1493 cm⁻¹.

Extractive metallurgy has recently turned its attention to waste treatment for the recovery of precious metals through innovative metallurgical processes, such as ion flotation. This work studied the influence of several chemical and physical factors, such as the concentration of xanthate [x], frother agent [e], dithiophosphate [xl], pH, superficial gas velocity Jg, percentage of gas holdup Eg, bubble diameter (Db) calculated with the drift flux model, and the type of sparger, in the efficiency of silver(I) recovery by the ion flotation technique in sub-aerated cells. The results obtained indicate a 90.7% v/v recovery of silver(I) under conditions of 3.77 × 10⁻⁴ M [x], 1.25 × 10⁻⁴ M [e], Jg 0.5 cm/s, Jl 0.19 cm/s, Eg of 4.1% v/v, and Optimal Db of 0.11 cm, with a rigid bubble generator, achieving an apparent flotation kinetics of 4.16 1/min. The use of combinations [x]–[xl] achieve a silver(I) recovery of 86.9% with a Jg of 1.0 cm/s. The best recovery efficiencies achieved 93% w/w silver(I) are with pH 8.0, [e] of 1.25 × 10⁻⁴, Jl of 0.19 (cm/s) and a rigid sparger compared to a flexible one.