VNIIKhT, Moscow, Russia:

I. D. Akimova, Lead Researcher, e-mail: akimid@rambler.ru
T. V. Molchanova, Head of Laboratory, e-mail: molchanovatv@vniiht.ru
R. S. Shchipanova, Lead Engineer

Titanovye Investitsii, Moscow, Russia:
V. V. Golovko, Deputy Manager of the Chemistry Department Responsible for New Projects, e-mail: golovko@tioinvest.ru

This paper describes the results of a study that looked at developing a technique to utilize sulfuric acid from the ilmenite processing waste at the “Titanovye Investitsii” site in Armyansk. The authors propose an extraction process that uses symmetrical tertiary amines as an extraction agent. An optimum composition of the extraction mixture was identified, which is 30% of trialkilamine + 20% of tributyl phosphate in kerosene. It was established that, in a standard multistage counter-current extraction process, a drop in the H₂SO₄ concentration to waste values would result in the precipitation of impurity metal hydroxides, which would impede the process. To ensure stable process parameters, a two-stage counter-current extraction process was developed for sulfuric acid extraction. The process implies a separate flow of extraction agent for each stage enabling to control the acid concentration at different process stages. Washing the leachate with a 300 g/dm³ sulfuric acid solution also leads to its fortification and rejection of impurities. In this process, the рН level in the resultant solutions does not exceed the impurity metal hydroxide precipitation pH. The sulfuric acid concentration in the waste drops from 300 to 1–10 g/dm³. The extraction raffinate, which contains ~10 g/dm³ of sulfuric acid, is considered a waste product and is utilized. The recovery of H₂SO₄ from the solution reaches 97–98%. The authors developed a process for re-extraction of sulfuric acid with ammonia liquor, which produces ammonium sulfate for use in agriculture. It was found that 280 kg of dry (NH₄)₂SO₄ salt can be produced from 1 m3 of hydrolytic sulfuric acid solution.

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