Selective recovery of zinc from goethite residue in the zinc industry using deep-eutectic solvents

Several deep-eutectic solvents (DESs) were tested for the valorisation of goethite residue produced by the zinc industry. The objective of the work was to selectively recover zinc from the iron-rich matrix using deep-eutectic solvents as lixiviants. The effect of the type of hydrogen bond donor and hydrogen bond acceptor of the deep-eutectic solvent on the leaching efficiency was studied. Levulinic acid–choline chloride (x_ChCl = 0.33) (LevA–ChCl) could selectively leach zinc from the iron-rich matrix, and it was selected as the best-performing system to be used in further study. The leaching process was optimised in terms of temperature, contact time, liquid-to-solid ratio and water content of the deep-eutectic solvent. The role of the choline cation on the leaching process was investigated by considering the leaching properties of a LevA–CaCl₂ mixture. The goethite residue was also leached with pure levulinic acid. The results were compared to a purely hydrometallurgical approach using sulphuric acid leaching. Leaching with LevA–ChCl resulted in higher selectivity compared to the conventional “hot leaching” with 80 g L⁻¹ sulphuric acid. Furthermore, a slightly higher zinc recovery and comparable selectivity for zinc over iron were achieved with LevA–ChCl compared to conventional “neutral leaching” with 10 g L⁻¹ sulphuric acid.

A mixture of levulinic acid and choline chloride can be used to selectively leach zinc from industrial residues with iron-rich matrices.     

Characteristics of differentiated CD8+ and CD4+ T cells present in the human brain

Immune surveillance of the central nervous system (CNS) by T cells is important to keep CNS-trophic viruses in a latent state, yet our knowledge of the characteristics of CNS-populating T cells is incomplete. We performed a comprehensive, multi-color flow-cytometric analysis of isolated T cells from paired corpus callosum (CC) and peripheral blood (PB) samples of 20 brain donors. Compared to PB, CC T cells, which were mostly located in the perivascular space and sporadically in the parenchyma, were enriched for cells expressing CD8. Both CD4⁺ and CD8⁺ T cells in the CC had a late-differentiated phenotype, as indicated by lack of expression of CD27 and CD28. The CC contained high numbers of T cells expressing chemokine receptor CX3CR1 and CXCR3 that allow for homing to inflamed endothelium and tissue, but hardly cells expressing the lymph node-homing receptor CCR7. Despite the late-differentiated phenotype, CC T cells had high expression of the IL-7 receptor α-chain CD127 and did not contain the neurotoxic cytolytic enzymes perforin, granzyme A, and granzyme B. We postulate that CNS T cells make up a population of tissue-adapted differentiated cells, which use CX3CR1 and CXCR3 to home into the perivascular space, use IL-7 for maintenance, and lack immediate cytolytic activity, thereby preventing immunopathology in response to low or non-specific stimuli. The presence of these cells in this tightly regulated environment likely enables a fast response to local threats. Our results will enable future detailed exploration of T-cell subsets in the brain involved in neurological diseases.