Gipronickel Institute, St. Petersburg, Russia

P. M. Saltykov, Senior Researcher, Finished Products Laboratory, e-mail: SaltykovPM@nornik.ru
Yu. N. Lisakov, Head, Finished Products Laboratory, Candidate of Technical Sciences, e-mail: lisakovYuN@nornik.ru
E. G. Saltykova, Lead Engineer, Finished Products Laboratory, e-mail: SaltykovaEG@nornik.ru
N. P. Chuprynin, Research Associate, Finished Products Laboratory, e-mail: chupryninNP@nornik.ru

The results of an experimental study of the neutralization of industrial sulfuric acid with natural limestone under various process conditions are presented. For the studies, the initial limestone, with pieces up to 60 mm in size, was crushed in a laboratory jaw crusher to a size of 1–5 mm. The crushed material was wet-milled in a laboratory ball mill to a size of –150 μm. The content of –70 μm particles in the crushed limestone was 86.9%. For each neutralization process mode, the process stability parameters were determined. During the experiments, the limestone consumption (1.10–1.50 kg/kg sulfuric acid), the solids content of the initial limestone pulp (125–200 g/l), and the pulp mixing speed (400, 800 min^–1) were varied. To confirm the process parameters obtained in the laboratory setup, an experiment was conducted on the continuous neutralization of sulfuric acid with limestone pulp on a pilot plant. The setup consists of three reactors installed in series, each with a working volume of 57–59 dm3. The cascaded arrangement of the reactors ensures the flow of pulp from each reactor to the next through overflows. It was established that the sulfuric acid neutralization process can be implemented in both batch and continuous modes. Possible safe neutralization modes are presented, along with an estimate of the reactor equipment packages required to implement the proposed mode. The most preferred neutralization mode without excessive foaming under conditions of high sulfuric acid production rates is a continuous mode, characterized by a reduced risk of pulp blowout due to foaming and a smaller volume of required reactor and mixing equipment. Continuous operation of the process allows for an increase in gypsum particle size, which, in turn, improves the sedimentation properties of the sludge.

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