Nickel metal hydride (NiMH) batteries are extensively used in the manufacturing of portable electronic devices as well as electric vehicles due to their specific properties including high energy density, precise volume, resistance to overcharge, etc. These NiMH batteries contain significant amounts of rare earth metals (REMs) along with Co and Ni which are discarded due to illegal dumping and improper recycling practices. In view of their strategic, economic, and industrial importance, and to mitigate the demand and supply gap of REMs and the limited availability of natural resources, it is necessary to explore secondary resources of REMs. Therefore, the present paper reports a feasible hydrometallurgical process flowsheet for the recovery of REMs and valuable metals from spent NiMH batteries. More than 90% dissolution of REMs (Nd, Ce and La) was achieved using 2 M H₂SO₄ at 75 °C in 60 min in the presence of 10% H₂O₂ (v/v). From the obtained leach liquor, the REMs, such as Nd and Ce, were recovered using 10% PC88A diluted in kerosene at eq. pH 1.5 and O/A ratio 1/1 in two stages of counter current extraction. La of 99% purity was selectively precipitated from the leach liquor in the pH range of 1.5 to 2.0, leaving Cu, Ni and Co in the filtrate. Further, Cu and Ni were extracted with LIX 84 at equilibrium pH 2.5 and 5, leaving Co in the raffinate. The developed process flow sheet is feasible and has potential for industrial exploitation after scale-up/pilot trails.

Non-availability of rich primary resources of rare earth metals (REMs) and the generation of huge amounts of discarded magnets containing REMs, compelled the researchers to explore the possibilities for the recovery of REMs from discarded magnets. Therefore, the present paper reports the recovery of REMs (Nd, Pr, and Dy) from discarded Nd-Fe-B magnets. The process consists of demagnetization, pre-treatment, and hydrometallurgical processing to recover REMs as salt. Leaching studies indicate that 95.5% Nd, 99.9% Pr, and 99.9% Dy were found to be dissolved at the optimized experimental condition i.e., acid concentration 2 M H₂SO₄, temperature 75 °C, pulp density 100 g/L, and mixing time 60 min. Solvent extraction technique was tried for the selective extraction/separation of REMs and Fe. The result indicates that 99.1% (24.42 g/L) of Nd along with 90% (1.08 g/L) of Pr and total Fe were co-extracted using 35% Cyanex 272 at organic to aqueous (O/A) ratio 1/1, eq. pH 3.5 in 10 min of mixing time. It requires multistage separation and therefore, not feasible in view of economics. Thus, direct precipitation of REMs salt and iron oxide as pigment was studied using two stages of precipitation at different pH. The obtained precipitate of REMs and Fe hydroxides were dried separately to remove the moisture and further treated at elevated temperature to get pure REMs oxide and red oxide.

Printed Circuit Boards (PCBs) are an essential component of electronic devices. The digitalization and upgrading of gadget generates lots of PCB-containing electronic waste. Conserving resources and protecting the environment requires the recycling of such e-waste. This paper focuses on the recovery of metals from waste PCBs using physical pre-treatment and hydrometallurgical processes. Initially, the waste PCBs were pre-treated and beneficiated to separate the metallic and non-metallic fractions. The metallic concentrate obtained was leached using nitric acid (a strong oxidative agent) to dissolve the metals. The system was fully jacketed with a scrubber and condenser to prevent the emission of toxic gases into the environment. The process parameters, such as the effect of acid concentration, pulp density, temperature, time, etc., were studied, optimized, and scientifically validated. The kinetics of leaching fitted well with the following shrinking core models: X_B = k_c.t for Cu, (1 − (1 − X_B)^1/2) for Ni, and 1 − 3(1 − X_B)^2/3 + 2(1 − X_B) for Pb. The activation energy was 19.42 kJ/mol. The tin left in the residue was treated separately. The developed process is useful for recovering metals from waste PCBs and has the potential to be commercialized after conducting scale-up studies.

Indium, widely used in indium–tin oxide (ITO) coatings for liquid crystal displays (LCDs), is a scarce and strategically important metal with increasing demand. Recycling waste LCD panels offers an efficient secondary source to address supply risks and environmental concerns. In this study, a hydrometallurgical flow sheet was developed under mild conditions for indium (In) recovery. Leaching trials with sulphuric acid at varying concentrations, pulp densities, temperatures, and times showed that 5% H₂SO₄ (v/v) with 100 g/L pulp density at 60 °C for 30 min achieved ~98% dissolution of In, while minimizing the co-leaching of Al and Sn. Kinetic analysis indicated a diffusion-controlled mechanism for In dissolution with an activation energy of 21.2 kJ mol⁻¹. The leached liquor was further purified through solvent extraction by 20% Cyanex 921 (v/v), achieving optimum In extraction at pH 2.5 with an organic-to-aqueous phase ratio of 1/3, reaching equilibrium within 15 min. The McCabe–Thiele plot shown indicates the complete In extraction in two stages. FT-IR studies confirmed the In-extractant bonding at optimized conditions. 10% H₂SO₄ (v/v) was used for the stripping of In from the loaded organic, ensuring nearly complete back-transfer of indium with excellent phase separation. The integrated process yielded ~97% In recovery in stripping. The pure salt of Indium could be obtained by evaporation/crystallization of pure indium solution. The developed process has the potential to be transferred for commercial exploitation after scale-up and pilot trial.

Printed Circuit Boards (PCBs) are essential to most electronic devices. Digitalization and upgradation of gadget generates lots of PCB-containing electronic waste. Conserving resources and protecting the environment requires recycling such e-waste. The present paper is focused on the recovery of metals from PCBs by physical pretreatment and hydrometallurgical processes. Initially, the waste PCBs were pre-treated to separate metallic and non-metallic fractions. The metallic concentrate was leached using nitric acid (strong oxidative agent) for dissolution of metals. The system was fully jacketed with scrubber and condenser so that no emission of toxic gases to the environment. The process parameters viz. effect of acid concentration, pulp density, temperature, time, etc. were optimized and the obtained data were scientifically validated. Kinetics leaching fitted well with the Shrinking core model, XB = kc.t for Cu, (1-(1-XB)1/2) for Ni and 1-3(1-XB)2/3 + 2(1-XB) for Pb. The optimized conditions derived from these studies will be useful for recovery of metals from waste PCBs, and tin left in the residue could be further treated for the purpose of safe disposal or the utilization in an environmentally friendly manner. The developed process provides environmental benefits and has potential to be commercialized after scale-up studies.