Elsevier

Hydrometallurgy

Volume 138, June 2013, Pages 14-20
Hydrometallurgy

Recovery of sulphuric acid from waste and process solutions using solvent extraction

https://doi.org/10.1016/j.hydromet.2013.06.005Get rights and content

Highlights

  • An optimum organic system consisting of 50% TEHA, 40% octanol and 10% Shellsol A150 for sulphuric acid extraction.

  • The acid extraction is exothermic with enthalpy change (ΔH) of − 13.2 kJ mol 1.

  • The extracted species consists of one acid, one TEHA (A) and two octanol (O) molecules with a formulae of H2SO4AO2¯.

  • The optimised TEHA system used to extracted acid from a synthetic process solution with metal removed by scrubbing

  • A conceptual process flowsheet developed using a combination of MD and SX to recover water, acid and metals.

Abstract

TEHA (tris-2-ethylhexylamine) was selected as the extractant in the current study due to high acid extraction and ease in stripping. An optimum organic system consisting of 50% TEHA, 40% octanol and 10% Shellsol A150 was determined. It was found that the acid extraction decreased with the increase in temperature. The change in enthalpy (ΔH) was − 13.2 kJ mol 1, indicating exothermic extraction reaction. Both extraction and stripping kinetics was very fast. McCabe–Thiele extraction diagram showed that for a feed solution containing 200 g/L H2SO4, three stages are required. McCabe–Thiele stripping diagram showed that three stages are required. Using slope analysis, it was found that the extracted species consisted of one acid molecule, one TEHA (A) molecule and two octanol (O) molecules with a formulae of H2SO4AO2¯.

The optimised TEHA system was used to extracted acid from a synthetic process solution containing a number of metals. It was found that the system only extracted acid with a small amount of metals entrained. After scrubbing the loaded organic solution in a single contact, almost all entrained metals were removed. In the case that the mining waste solution contains low concentration of acid, membrane distillation (MD) technology can be used to recover the water and concentrate the acid and metals. Solvent extraction can be then used to recover the acid and metals. A conceptual process flowsheet has been developed using a combination of MD and SX.

Introduction

Solvent extraction (SX) is a well established technology to separate, purify and concentrate metals. It has been also applied for acid recovery from waste solutions and bleeding streams of copper, zinc and precious metals (Agrawal and Sahu, 2009, Agrawal et al., 2007, Agrawal et al., 2008, Gottliebsen et al., 2000a, Gottliebsen et al., 2000b). The use of SX to recover various acids has been reviewed by Ritcey (2006).

Extractants including TEHA (tris-2-ethylhexylamine), Alamine 336 (tri-octyl/decyl amines), TBP (tributyl phosphate) and Cyanex 923 (hexyl/octyl phosphine oxides) have been tested and applied to recover acids using solvent extraction (Agrawal et al., 2007, Alguacil and Lopez, 1996, Gottliebsen et al., 2000a, Gottliebsen et al., 2000b, Liao et al., 2002, Rickelton, 1993, Sarangi et al., 2006). Agrawal et al. (2008) studied the extraction of sulphuric acid from zinc electrowinning bleed stream containing 174 g/L H2SO4 using TEHA in kerosene. It was found that TEHA had very good acid extraction capacity even in the presence of a large amount of zinc. In a similar study, Haghshenas et al. (2009) investigated the extraction of sulphuric acid in terms of thermodynamics and other conditions. It was reported that the acid extraction increased with the increase in the TEHA concentration in the organic solution and reached a maximum depending on the initial acid concentration in the feed solution. Furthermore, a comparison of TEHA and Cyanex 923 for sulphuric acid extraction was studied in terms of thermodynamics. It was found that stripping of sulphuric acid from TEHA is more readily than from Cyanex 923 while the stripping of acid was easier from Cyanex 923 than from amine extractants (Wolter et al., 2002). Agrawal et al. (2007) studied the extraction of sulphuric acid using Alamine 336 and found that the extraction of sulphuric acid increased with the increase in the Alamine 336 concentration. Although, Alamine 336 showed higher extraction ability for sulphuric acid than Cyanex923, the acid extracted could not be stripped completely using hot water.

The acid concentrations in mining waste solutions are usually low and can be concentrated using membrane distillation (MD) technology in which the vapour of volatile constituents including water in the feed solution of the hot side can pass through the pores of the hydrophobic membrane to the cold side for condensation. As a result, fresh water is recovered and the other constituents are concentrated. MD offers advantages of low energy consumption, high efficiency and operating at low temperatures to recover fresh water and concentrate the acid and metals (Tomaszewska, 2000, Tomaszewska et al., 1995). After concentrating, solvent extraction can be applied to selectively recover the sulphuric acid and valuable metals.

In the current paper, the most suitable extractant for sulphuric acid recovery in terms of extraction and stripping was selected, optimised and characterised. The composition of the extracted species was investigated using slope analysis and a process flowsheet to recover water, acid and metals proposed.

Section snippets

Organic solutions

Organic solvents TEHA and octanol were purchased from Sigma-Aldrich. Alamine 336 was supplied by BASF, Cyanex 923 by Cytec and Shellsol A150, Shellsol 2046 and Shellsol D70 by Shell Chemicals, Australia. All reagents were used without further purification.

Aqueous solutions

The feed solution containing only sulphuric acid was prepared by diluting AR grade concentrated sulphuric acid using deionised water. The feed solution containing sulphuric acid and metals was prepared by adding required amounts of AR grade

Selection of organic system in terms of extraction

Three organic extractants including TEHA, Alamine 336 and Cyanex 923 were used to extract acid in the feed solution containing 200 g/L H2SO4 at an O/A ratio of 2 and 22 °C. Preliminary experiments were performed using extractants in the concentration range of 20–60% (v/v) TEHA and Alamine 336 and 20–100% (v/v) Cyanex 923 (Table 1). Initially, octanol was used as the diluent for all three systems. For the Alamine 336 system, gel was formed with octanol as the diluent. Agrawal et al. (2007) met the

Conclusions

Three extractants for the recovery of sulphuric acid from acidic waste solutions were tested including TEHA, Alamine 336 and Cyanex 923. Amongst the three extractants, TEHA performed best in terms of acid extraction and stripping. Therefore, the TEHA system was selected for optimisation.

A number of diluents and modifiers were tested with various TEHA concentrations. An optimum organic composition consisting of 50% TEHA, 40% octanol and 10% Shellsol A150 was determined. The acid extraction

Acknowledgements

Drs Zhaowu Zhu and Goutam Das and Mr Yoko Pranolo are thanked for assisting test work. One of the authors (U. Kesieme) would like to thank CSIRO and Victoria University for providing PhD scholarships. The support of CSIRO Process Science and Engineering and CSIRO Minerals Down Under National Research Flagship is gratefully acknowledged.

Cited by (49)

  • Recovery approaches for sulfuric acid from the concentrated acid hydrolysis of lignocellulosic feedstocks: A mini-review

    2021, Energy Conversion and Management: X
    Citation Excerpt :

    Salts, although mainly reporting to the aqueous phase, can be entrained to the organic phase to some degree during solvent extraction. Kesieme et al. [49,50] utilized a scrubbing step to remove these salts from the organic phase prior to acid stripping Jansen et al. [52] prevented build-up of compounds in the organic solvent system, such as furans, organic acids, soluble lignin compounds and esters, by treating a part of the recycled organic stream with a 10% lime slurry at 80 °C, which effectively removed these compounds.

View all citing articles on Scopus
View full text