LUT University, School of Engineering Science, Department of Separation Science, Yliopistonkatu 34, FI−53850 Lappeenranta, Finland
2 LUT University, School of Engineering Science, Department of Separation Science, Yliopistonkatu 34, FI−53850 Lappeenranta, Finland
Oxalic acid is one crucial reducing agent in hydrometallurgical processes, and it is used in an excess stoichiometric amount for precipitation of valuable metals. Significant amount of oxalic acid with a small content of metals may be created as a side stream. The extraction of oxalic acid from these side streams can 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 oxalic acid recovery from hydrochloric acid solution with Tributyl phosphate (TBP) and Cyanex923 as solvating reagents and Trioctylamine (TOA) and Trioctylmethylammonium chloride (Aliquat336) as tertiary and quaternary amines. First, batch experiments were conducted and the effect of extractant concentration, time, and temperature were studied. Preliminary results showed that TBP, Cyanex923 and Aliquat336 had high affinity and capacity to oxalic acid, but TOA extracted more than 95% of both acids in single stage of extraction which means that this solvent was not practical for selective extraction of oxalic acid. TBP, Cyanex923 and Aliquat336 were selected for loading and stripping isotherm experiments for determining initial design for counter-current stages and amount of organic (O/A ratio) required of oxalic acid recovery. The results of McCabe-Thiele diagram revealed that the effectiveness of extracting oxalic acid using 1.45M TBP and 0.127M Cyanex923 in three counter-current stages was 96.2% and 93.4%, respectively. Furthermore, four counter-current stripping stages of loaded TBP and Cyanex923 resulted in 95.5% and 95.2% yields, respectively. In contrast, using 1.34M Aliquat336 resulted in less favorable extraction and stripping yields, 81.7% and 89.1% respectively, indicating that Aliquat336 is not as effective as TBP and Cyanex923 reagents. The results of this paper demonstrate the promising potential of the designed solvent extraction process for recovering pure oxalic acid and hydrochloric acid streams for re-use in hydrometallurgical plants, leading to enhanced both the environmental and economic efficiency of such plants.