Reductive atmospheric acid leaching of lateritic smectite/nontronite ores in H2SO4/Cu(II)/SO2 solutions

Abstract

Despite the success of reductive atmospheric acid leaching (RAAL) of limonitic nickel laterite ores in recent studies limited attempt has been made to apply this method to smectite/nontronite ores of different mineralogy. A comparative study of four smectite/nontronite ores in this study showed that the use of 700 kg H 2 SO 4 /ton dry ore leaches only 74-86% Ni, 37-76% Co, 47-58% Fe and 24-66% Mn at 90 o C from slurries of 20-35% (w/w) pulp density even after 10 h, depending upon the mineralogy. These values increased to 90-97% Ni, 94-97% Co, 92-98% Mn and 72-85% Fe in the presence of Cu(II)/SO 2 . The first order dependence of initial fraction of iron, aluminium and nickel leached from a typical smectite ore in the first 0.5 h on the initial acid concentration provide evidence for the involvement of hydrogen ions in the surface reaction. Low activation energy of 10 kJ/mol based on the fraction of nickel leached in the first 0.5 h indicates a diffusion controlled reaction. This is supported by the applicability of a shrinking core kinetic model for metal dissolution over the first 2 h, with different apparent rate constants (k ap ) depending upon the iron oxide content, mineralogy and porosity. A log-log plot of k ap for ores with high iron content as a function of acid concentration agrees reasonably well with the correlation already established for the leaching of nickel from limonitic laterite and manganese nodules. Thus, initial fast leaching can be related to the higher porosity and a rate controlling step which involves the diffusion of H + through a thickening solid layer. The slow leaching at latter stages is a result of low remnant acid, thickening solid layer and changes in mineral composition.

Correlation of Nano Titanium Dioxide Synthesis and the Mineralogical Characterization of Ilmenite Ore as Raw Material

“…Likewise, the calculated value of D H + for titanium dissolution is 0.3 x 10 -10 cm 2 s -1 . The order of these values in the range of 3 x 10 -11 to 13 x 10 -11 cm 2 s -1 are at the high end of the range of 10 -11 -10 -15 cm 2 s -1 for previously reported values of D H + relevant to the dissolution of different minerals based on the diffusion through product layers (Georgiou and Papangelakis, 1998;Senanayake and Das, 2004;Senanayake et al, 2015) indicating the different porosities of such layers.…”

“…This model can be expressed in the form of Eq. 2.8 a, b (Levenspiel, 1972;Senanayake and Das, 2004;Senanayake et al, 2015) in which X = the fraction dissolved at time t, k pl = apparent rate constant, [H + ] = concentration of acid in bulk solution (mol cm -3 ), D = diffusion coefficient of H + through the product layer (cm 2 s -1 ), r = initial particle radius (cm), ρ = molar density of the dissolving metal in the initial particle (mol cm -3 ), b = stoichiometric factor and ε = particle porosity.…”

Hydrometallurgical Nickel and Cobalt Production From Lateritic Ores: Optimization and Comparison of Atmospheric Pressure Leaching and Pug-Roast-Leaching Processes

“…Contaminants such as Fe, Al, Cr, Mn and Mg, other than nickel and cobalt, are removed by precipitation of these elements and/or separation of nickel and cobalt from the solution to produce nickel and cobalt. Pug-roast-leaching processing can be used as an alternative method for the dissolution of lateritic ore at atmospheric pressure by using sulfuric acid [29][30][31][32][33][34][35][36]. This can be considered as an improved version of the atmospheric pressure sulfuric acid leaching due to the fact that water insoluble oxides are converted to water soluble sulphates.…”

“…This can be considered as an improved version of the atmospheric pressure sulfuric acid leaching due to the fact that water insoluble oxides are converted to water soluble sulphates. Considering all the above factors, it was decided to use pugroast-leaching process in the experimental studies in order to see how these processes could be improved and how the disadvantageous sides could be eliminated of atmospheric pressure acid leaching process [27][28][29][30][31][32][33][34][35][36]. The aim of this study is to determine the optimum parameters for nickel and cobalt production from limonite type lateritic nickel ores, which were taken from Manisa Caldag region of Turkey, through atmospheric pressure sulfuric acid leaching and pug-roast-leaching processes.…”

Leaching of Germanium from Zinc Residue in H<sub>2</sub>SO<sub>4</sub>/SO<sub>2</sub> Solutions

“…Due to the strong reducing nature of Sulfur dioxide (SO 2 ), it is an efficient leaching agent for minerals containing oxides of iron, nickel, cobalt and manganese [7][8][9][10][11][12][13]. Studies have been reported on SO 2 accelerated leaching of various natural and synthetic iron oxides such as magnetite (Fe 3 O 4 ), goethite (a-FeOOH), hematite (Fe 2 O 3 ) and nickel/cobalt spiked goethite at atmospheric pressure [8,12,[14][15][16][17][18]. The main reactions occurred: 3 In this work, a typical zinc residue with high germanium content has been used for reduction leaching studies in the presence of gaseous SO 2 .…”