Co(II) and Ni(II) transport from model and real sulfate solutions by extraction with bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272)

This paper presents the results of Co(II) and Ni(II) extraction from model and real solutions using bis(2,4,4-trimethylpentyl)phosphinic acid (i.e. Cyanex 272) that are in agreement with waste-to-resources approach, i.e. the recovery of valuable components from wastes. The results from this study shows that, extraction using Cyanex 272 is an efficient method to recover Co(II) selectively from sulfate electrolytes obtained from the leaching of steel scraps of aircraft engines. The highest selectivity value (∼160) of Co(II) extraction over Ni(II) was obtained at a pH of 4.8, the lowest selectivity value (∼30) was observed at a pH of 5.5, while above this value the selectivity only increased slightly with increasing pH. A pH of 5.2 was selected as a compromise between Co(II) selectivity and Ni(II) amount in the organic phase. The essence of the investigation is to propose important parameters to extract Co(II) from real leach solutions, and to further recover valuable Co(II) from the loaded organic phase by stripping with 1 M H₂SO₄, thus producing an electrolyte of Co(II) for electrowinning - a possible alternative route for resource recovery. Small volume of the stripping phase (w/o = 1:5) used in this study, lead to an enrichment of sulfate electrolyte in Co(II), resulting in ∼50 g/dm³ of Co(II) in the solution, which is a great advantage of the approach proposed. Such a solution is a valuable source for the electrowinning of metallic cobalt, which can be used for the production of steel alloys, Li-ion batteries or catalysts.

Electroplating wastes

Electroplating and other metal finishing industries, like every metal and metallurgical industry, are associated with the generation of waste. Spent electroplating baths, waste pickle liquors, etching solutions and rinse waters from electroplating units and steel finishing operations are complex solutions containing acids and several hazardous metals. It is compulsory, for environmental and economic reasons, to treat these solutions for recovering acid, metals and/or reusing these solutions/waters. This article is a review on the characterization of the wastes that are generated in electroplating industry, steel processing and copper etching in printed circuit boards manufacture, as well as on the treatment and regeneration methods of such streams. Various techniques, such as neutralization, crystallization, evaporation, pyrohydrolysis, electrodialysis, ion exchange, classical solvent extraction and membrane-based solvent extraction are presented, their advantages and disadvantages being scrutinized.

Oxidative degradation of bis(2,4,4-trimethylpentyl)dithiophosphinic acid in nitric acid studied by electrospray ionization mass spectrometry

RATIONALE

The selective separation of the minor actinides (Am, Cm) from the lanthanides is a topic of ongoing nuclear fuel cycle research, and dithiophosphinic acids are candidate ligands in these processes. Ligand instability has been noted under radiolytic and harsh acid conditions but explicit degradation pathways for ligands such as bis(2,4,4-trimethylpentyl)-dithiophosphinic acid (CyxH), the major compound in the commercial product Cyanex 301, have been elusive.

METHODS

Organic solutions of CyxH were contacted with aqueous solutions of HNO(3), and their degradation was studied by analyzing samples from these experiments by direct infusion electrospray ionization mass spectrometry. Ions were identified using accurate mass measurement and collision-induced dissociation.

RESULTS

The positive ion spectra contained cationized CyxH cluster ions, and oxidatively coupled species (designated Cyx(2)) cationized by either H or Na. The Cyx(2)-derived ions increased with acid contact time. The negative ion spectra consisted almost entirely of the CyxH conjugate base. The negative ion spectra of the HNO(3)-contacted samples also contained conjugate bases corresponding to the dioxo and perthio derivatives of CyxH.

CONCLUSIONS

CyxH is oxidized by acid contact to form the coupled species Cyx(2), and the dioxo species arise from subsequent oxidation of Cyx(2). Oxidative coupling increases with contact time, and with higher HNO(3) concentrations. The direct infusion measurements provided a simple approach for assessing degradation pathways and kinetics.

Separation of monovalent and divalent ions from aqueous solution by electrodialysis and nanofiltration

The possibilities of separating monovalent and multivalent ions by electrodialysis (ED) and nanofiltration (NF) are explored. Five synthetic single salt solutions were applied to ED and NF: NaCl, Na(2)SO(4), MgCl(2), MgSO(4) and NaNO(3). Two combinations of anionic and cationic exchange membranes were evaluated for ED (AMV/CMV Selemion membranes and ACS/CMS Tokuyama membranes), and two membranes were evaluated for NF (NTR 7450 and UTC-60). The separation was evaluated using an alternative parameter, the separation efficiency, in order to compare ED and NF. The separation efficiency ranges from 0% (no separation) to 100% (perfect separation). Both NF membranes had a good separation efficiency for the separation of monovalent and divalent anions (ca. 60%); the ED membranes performed worse. For the separation of monovalent and divalent cations, the UTC-60 membrane was the best for the considered separation because of size exclusion effects for the larger divalent ion. The ACS/CMS membranes had a similar separation efficiency (ca. 60%); the NTR 7540 membrane and AMV/CMV ED membranes showed only a small separation.