2024

Aref Reza; Jantunen Niklas; Virolainen Sami

Oxalic acid is a crucial precipitation and reducing agent in hydrometallurgical processes, and significant amounts of oxalic acid with a small content of metals are created as side streams. The extraction of oxalic acid from these side streams would have both economic and environmental benefits. Economically, it can provide a valuable source of revenue, and environmentally, it can reduce the amount of waste. In this research, the aim was to investigate recovery of 10.2 g l-1 of oxalic acid from 37.5 g l-1 hydrochloric acid solution containing 1.1 g l-1 Co with tributyl phosphate (TBP), trialkyl phosphine oxides (CYANEX 923), trioctylamine (TOA), and trioctylmethylammonium chloride (Aliquat 336) extractants. The effects of extractant concentration, equilibration time, and temperature were investigated in batch experiments. Oxalic acid distribution coefficient was improved as temperature was increased with CYANEX 923 and Aliquat 336 reagents, whereas was decreased when using TBP. Also, fast extraction kinetic obtained with both TBP and CYANEX 923 reagents, and the equilibrium was achieved within 1 min. The results of the equilibrium studies and McCabe-Thiele analysis theoretically showed that the effectiveness of extracting oxalic acid using 1.83 M TBP, 0.25 M of CYANEX 923, and 1.09 M Aliquat 336 in three counter-current stages would be 96.2%, 93.4%, and 88.2% respectively. Furthermore, four counter-current stripping stages with pure water would results in 95.5%, 88.4%, and 89.1% yields, respectively. Continuous counter-current experiments in a bench-scale mixer-settler cascade were performed with 1.83 M of TBP to investigate the effect of number of stages (N), residence time in mixer (t mix) and phase ratio (O/A) on the extraction and stripping efficiency of oxalic acid. Over 99% of oxalic acid was extracted from the feed solution using a O/A =1:1, t mix = 1 min, N = 4, and at T = 20 ± 1 °C. The co-extraction percentages for HCl and Co were 14.6% and 5.1%, respectively. 94.0% of the oxalic acid could be stripped from the loaded reagent using pure water with O/A = 1:2, t mix = 1 min, N = 4, and at T = 20 ± 1 °C. Overall, the results of this work demonstrate the potential of the designed solvent extraction process for recovering of oxalic acid with a purity of 98.55% starting with HCl containing Co as the feed solution.