THE EXTRACTION OF ARSENIC (Ⅴ) AND SULPHURIC ACID FROM ACIDIC SULPHATE MEDIA BY TRI-N-BUTYL PHOSPHATE (TBP) IN SHELLSOL A OR T∶ I - AN EQUILIBRIUM STUDY

摘要

The composition of the sulphuric acid and arsenic(Ⅴ) species extracted by tri-n-butyl-phosphate (TBP), in either Shellsol A (aromatic) or Shellsol T (non-aromatic) diluent, from aqueous media, containing either H_2SO_4 alone or both H_2SO_4 and As(Ⅴ) was studied by slope analysis. Other extractants, including amines, did not extract much As(Ⅴ). The average compositions of the H_2SO_4 species for 1.8-3.66 mol/L TBP from pure 1-5 mol/L H_2SO_4 were (TBP)_3(H_2O)_5H_2SO_4 and (TBP)_4(H_2O)_6H_2SO_4 in Shellsol T or A, respectively. With As(Ⅴ) present the extracted species were similar but less H_2SO_4 was extracted. The As(Ⅴ) species extracted from 0.25-4 mol/L H_2SO_4 were (TBP)_3H_3AsO_4 in Shellsol T or (TBP)_5H_3AsO_4 in Shellsol A. The enthalpy of extraction was estimated to be -26.6 kJ/mol from the variation with temperature (12-33.5°C). As(Ⅴ) extraction decreased slightly as the pH increased from 0.3 to 1.6.