Rhenium adsorption from an organic impurity–containing solution

Modern rare metal production technologies involve the liquid extraction of target components using organic compounds. This inevitably leads to environmental contamination and often increases the costs of obtaining the final product at the required purity. The purpose of this study was to design a sustainable adsorbent for the selective removal of organic impurities and rhenium from realistic production solutions. To prepare this adsorbent, waste from special coke production (special coke fines (FSC) without any additional processing) and rice husk pyrolysed at 450 °C for 30 min were used. The pyrolysed rice husk was subsequently activated with water vapour and then treated with an alkaline solution. The raw materials were studied using chemical analysis, elemental analysis, and SEM. The adsorption properties of adsorbents with respect to organic impurities and rhenium were studied in batch and column modes. Fresh and spent adsorbents were investigated using SEM, EDS, WDS, and IR spectroscopy. GC‒MS analysis was used to determine the composition of the organic impurities in the solutions before and after the sorption process. FSC selectively removed organic impurities, with the degree of rhenium extraction remaining below 1%. The full dynamic exchange capacity (FDEC) for organic impurities was 22.5 mg g⁻¹. The rice husk–based adsorbent was characterised by high adsorption activity for rhenium ions: a static exchange capacity (SEC) of 9 mg g⁻¹, an extraction degree of 90%, and a distribution coefficient of 1005 cm³ g⁻¹. The adsorption of Re on the rice husk–based adsorbent proceeded favourably and was best described by the Langmuir isotherm model (R2 = 0.998) and a pseudo-second-order kinetic model (R2 = 0.998). Column mode was used to establish a solution containing 640 mg dm⁻³ Re and 764 mg dm⁻³ organic impurities such that the full dynamic exchange capacity of the rice husk–based adsorbent for rhenium was 120 mg g⁻¹ following the purification of organic impurities with FSC. According to the results of IR spectroscopy, rhenium is adsorbed in the form of Re—O. Overall, adsorbents obtained from agricultural and industrial waste hold promise as sustainable and cost-effective materials for rhenium recovery from solutions containing organic impurities.