Immobilization capacity assessment of a binder from arsenic-containing biohydrometallurgy waste: Effects of halloysite nanotubes and biochar addition

The aim of this study was to improve the immobilization capacity of a binder prepared from As-containing biohydrometallurgy waste (BAW) on arsenic (As) by modifying it with halloysite nanotubes (HNTs) and biochar (BC). The study investigated the influence of HNTs and BC on the chemical fractions and leaching characteristics of As, as well as the influence on the compressive strength of BAW. The results indicated that the addition of HNTs and BC effectively decreased As leaching. The presence of 1.0 wt% HNTs decreased the As leaching concentration from 1.08 mg/L to 0.15 mg/L, with the corresponding immobilization rate reaching about 90.9 %. A high amount of BC seemed to show better performance in improving the As immobilization capacity of BAW. However, a strongly reduced early compressive strength of BAW was observed, making it unsuitable to be used as an additive in this situation. The effects of HNTs on the increase of As immobilization capacity of BAW were attributed to two aspects. Firstly, As species were adsorbed onto the surface of HNTs via H-bonds, which was verified via density functional theory calculation. Secondly, the addition of HNTs decreased the pore volume of BAW, leading to a more compact structure, and hence increasing the physical encapsulation capacity for As. Environmental implication: The rational disposal of arsenic-containing biohydrometallurgy waste has always been a top priority for the green and low-carbon development of the metallurgical industry. In this article, we have taken the perspective of large-scale resource utilization of solid waste and pollution control, and developed arsenic-containing biohydrometallurgy waste into a cementitious material, and enhancing arsenic immobilization capacity with the addition of HNTs and BC. This study provides an effective method for the rational disposal of arsenic-containing biohydrometallurgy waste.