Modification of bio-based β-diketone from wheat straw wax : synthesis of polydentate lipophilic super-chelators for enhanced metal recovery

Bio-derived lipophilic polydentate chelators have been synthesized and tested for their chelating ability using a range of metal salts of Cu, Co, Ni, Fe, and Cr. These novel molecules were produced by the Michael addition reaction of 14,16-hentriacontanedione, isolated from wheat straw wax, with methyl acrylate or bio-derived dimethyl itaconate via microwave heating. The Michael adducts could either be used directly as esters or be hydrolysed to their acid form. Critically, the creation of additional binding sites via the carboxylate moieties leads to an enhanced metal uptake over both a non-renewable commercially available lipophilic β-diketone (dibenzoylmethane) and the unmodified hentriacontane-14,16-dione, for the chelation of Fe(iii), Cr(iii) and Ni(ii). The modified β-diketone containing a single carboxylic acid functionality was able to extract 167 mg L−1 of Fe(iii) from an FeCl3 solution with no pH adjustment. In comparison, no chelation was observed with dibenzoylmethane, while unmodified hentriacontane-14,16-dione was able to extract 81 mg L−1. The modified chelators containing one and two ester carboxylates extracted 255 and 305 mg L−1 Cr(iii) from a solution of CrCl3 at pH 5-6, 238 mg L−1 was extracted by the unmodified β-diketone whilst no extraction was observed using dibenzoylmethane. This suggest some minor contribution or positive effect to chelation due to neighbouring ester groups. The chelator containing two carboxylic acid groups (tetra-dentate when combined with the diketone) was the most proficient in this study for removal of Ni from an NiCl2 solution (140 mg L−1). It was also found that at higher pH almost quantitative extraction was achieved using the polydentate chelators

The evolution of mineral processing in extraction of rare earth elements using solid-liquid extraction over liquid-liquid extraction: A review

This review paper summarises the fundamental in the production of rare earth elements (REE) specifically on the extraction of REE. Liquid-liquid extraction (LLE) is known to be the most common method employed in the extraction of REE. However, it possesses a few disadvantages by having poor contact area and the formation of third phase during the extraction process. Solid-liquid extraction (SLE) compensates most of the disadvantages in LLE such as the formation of third phase and poor contact between extractant and desired elements. The focus of this paper is to review the evolution of REE extraction and discovers the potential of REE extraction through SLE. Extractants are available widely but when assisted by supporting material via immobilisation, theoretically it elevates the contact area between extractant and desired REE and this concept is known as extractant immobilised material (EIM). The graphical abstract illustrates the concept of EIM between extractant immobilised supporting materials which increases the potential of REE being extracted from aqueous phase. The material is not limited to polymeric resin, silica and membrane, but also microorganism, bio-derived and hybrid materials. EIM is expected to enhance the contact surface area, avoid third phase formation, and reduce the use of chemicals thus increasing the extraction and selectivity of REE. Also, EIM in SLE has the potential to surpass the conventional method in LLE in terms of quantity and quality