Empirical Model to Estimate Mn 2+ Precipitation Rate from a Leaching Solution Using SO 2 /O 2 as Oxidizing Agent
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Empirical Model to Estimate Mn2+ Precipitation Rate from a Leaching Solution Using SO2/O2 as Oxidizing Agent
S. Bello-Teodoro and R. Pérez-Garibay Centro de Investigación y Estudios Avanzados del IPN, Unidad Saltillo, Carretera Saltillo-Mty km 13.5, C.P. 25900, Ramos Arizpe, Coah., México. E-mail: [email protected]
ABSTRACT A method, based in leaching with SO2, to process low grade pyrolusite minerals has shown good results at laboratory scale. After the separation of the solid impurities, the dissolved manganese is subsequently precipitated using the SO2/O2 gas mixture as oxidising agent. In this research it was obtained a mathematical model to estimate the oxidative precipitation process, as a function of temperature, pH and SO2 gas flow rate. It was found that pH and temperature have the main influence in the reaction rate. An optimal SO2 concentration in the mixture must be used to avoid generation of reductive conditions. It was observed a most efficient reaction with a low gas flow rate injection. The predicted reaction rates presents a good concordance with the experimental results (R2=0.97), showing a worthy potential for practical uses. Keywords: Manganese precipitation; manganese oxidation.
INTRODUCTION Manganese is an important element in the steel industry because of its utility in deoxidising and desulphurisation. Specifically, it allows the formation of manganese sulphide and avoids the formation of interstitial ferric sulphide. Moreover, manganese sulphide increases the fracture resistance during the lamination of steel at high temperatures. Of the manganese added to steel, about 30% is added because of its properties as sulphide former and deoxidant, while the other 70% is added purely as alloying element [1]. Manganese is also added to aluminium and copper
alloys and, recently, there has been an increase in the use of manganese dioxide in the production of batteries. In manganese-producing countries, this increased demand has led to the processing of ores with a low metal grade. The SO2-O2 system has been studied and has demonstrated its efficiency as oxidising agent [2, 3]. It is well known that pure sulphur dioxide is a reducing agent used in a wide range of industries. However when combined with oxygen over a particular range of compositions, and in presence of certain transitions metals, sulphur dioxide acts as a stronger oxidising agent than oxygen [3]. The elimination of manganese impurities from leached solutions of cobalt, nickel and zinc is the most common objective of manganese precipitation with a SO2/O2 gas mixture [4-8]. An empirical rate equation for the partial removal of manganese from solutions using a SO2/O2 gas mixture was obtained [9]. The studied variables were the gas composition, the concentrations of dissolved sulphur and O2, and the solution temperature and pH. The relationships between the rate of manganese precipitation and each of these parameters were obtained from batch tests using a manganese sulphate synthetic solution. The reported Equation is:
(1)
with
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