Leaching of Manganiferous Ores by Glucose in a Sulfuric Acid Solution: Kinetic Modeling and Related Statistical Analysis F. Veglio ` ,* ,† M. Trifoni, ‡ and L. Toro ‡ Dipartimento di Ingegneria Chimica e di Processo, Facolta ` di Ingegneria, Universita ` degli Studi di Genova, via Opera Pia, 15, 16145 Genova, Albaro, Italy, and Dipartimento di Chimica, Facolta ` di SMFN, Universita ` degli Studi “La Sapienza”, P.le A. Moro, 5-00185 Roma, Italy A kinetic study of a manganiferous ore leaching in acid media by glucose as the reducing agent is here reported. The shrinking-core model opportunely modified was used to describe the kinetics of the manganese dissolution. Considering the complex network of chemical reaction involved in this process, a variable activation energy term was introduced in the kinetic model to take into consideration the different chemical reaction evolution. A nonlinear regression analysis was performed in order to estimate the modeling parameters, and their related statistical analysis was carried out as well. The proposed model was verified at low and high ore content (10 and 200 g/L, respectively). This comparison showed a quite good agreement between the experimental data and the theoretical prevision, confirming the possible application of the estimated kinetic parameters in a wide range of ore content. 1. Introduction Leaching is one of the central unit operations in the hydrometallurgical processes. A careful kinetic study concerning the controlling reaction step(s), the factors kinetically influencing the metal extraction yield and the estimation of the modeling parameters becomes very important for an efficient design process of hydro- metallurgical operations. Several kinetic models relating the metal extraction yield to the leaching time are shown in the literature. 1-5 As is known, one of the most useful mathematical models used to represent the kinetics of noncatalytic heterogeneous reactions is the shrinking-core model (SCM). 6 In the present work the acid leaching of manganese dioxide ores by using glucose as the reducing agent was kinetically studied by using the SCM opportunely modified. The overall chemical reaction which takes place during the leaching treatment is reported in the follow- ing: As is shown elsewhere, 7 a complex network of reac- tions may be supposed by considering the carbohydrates behavior in an acid medium. In fact, although the stoichiometry reported in eq 1 can well represent the overall dissolution process, several steps of carbo- hydrates chemical degradation may be considered dur- ing the leaching treatment time. For this reason it should be necessary to monitor all of the components produced during the process to give a complete modeling description of the manganese dissolution during the leaching time. A previous study 8 showed that there is a relationship between the stoichiometry of the reaction (1) and the reagent concentrations: from the analysis of those experimental results, the presence of intermediate partially oxidized products slowing the reaction rate (because of worse reductants than glucose) was sup- posed and experimentally evaluated. 8 The existence of intermediate products in the reaction medium constitutes one of the uncertainties in the collection and interpretation of the leaching data. 9 For this reason a kinetic model able to describe a complex set of chemical reactions was considered of interest without needing a mathematical description for each intermediate reactive step. The aim of the present work was the evaluation of a suitable mathematical model to describe the reductive acid leaching of manganese dioxide by glucose consider- ing only the global chemical reaction (1) and using a standard mathematical modeling description (SCM) relating the activation energy with the manganese conversion dissolution. The use of this model was successfully employed in the pyrrhotite bioleaching process and may be useful in the kinetic modeling of a number of leaching/bioleaching processes. 10 2. Materials and Methods 2.1. Ore. The manganiferous ore used in the experi- mental tests comes from an Italian mine (Latium, Italy). The sampling of its size fractions employed in the tests was performed according to Gy’s rules to obtain representative samples for analysis. Table 1 shows the overall chemical composition of the investigated ore as metal oxides. 2.2. Experimental Procedures. Each batch test was performed in an Erlenmeyer flask with a screw plug placed in a thermostatic Dubnoff shaker. Ore, sulfuric acid, and glucose were placed in the shaken flask * Corresponding author. E-mail: veglio@unige.it or veglio@ ing.univaq.it. † Universita ` degli Studi di Genova. ‡ Universita ` degli Studi “La Sapienza”. C 6 H 12 O 6 + 12MnO 2 + 12H 2 SO 4 f 6CO 2 + 12MnSO 4 + 18H 2 O (1) 3895 Ind. Eng. Chem. Res. 2001, 40, 3895-3901 10.1021/ie0004040 CCC: $20.00 © 2001 American Chemical Society Published on Web 08/04/2001