Abstract
This work continues on from previous studies showing that mineral sequestration by carbonation of magnesium or calcium silicates under high pressure and high temperature can be successfully carried out by processing in an autoclave. The paper is focused on the influence of experimental parameters on avoiding scale formation during pre-treatment in an autoclave and a subsequent leaching. Amorphous silica and magnesite, respectively, were the main reaction products in a carbonation of olivine under high pressure conditions in an autoclave. In addition, the examined peridotites may be accompanied by small to medium amounts of nickel or other metals, the recovery of which will be investigated in the present study: Extraction of metals such as nickel, iron, and magnesium from olivine bearing ore using hydrochloric acid under atmospheric pressure was studied between 50 and 90 °C in 1 h. The obtained results have shown maximal leaching efficiency of about 35% for Ni, Fe, and Mg under atmospheric pressure, in comparison to more than 60% obtained under the same conditions after a carbonation pre-treatment in an autoclave. Silica gel was formed during leaching without a pre-treatment of peridotite blocking the leaching process, which is not the case for the pre-treated material. The influence of temperature, reaction time, particle size and pre-treatment of peridotite in an autoclave during carbonation at 175 °C and 71.5 bar was studied. A new mechanism model for metal extraction from olivine-bearing ore by avoiding silica gel formation during leaching with hydrochloric acid including a carbonation pre-treatment is proposed. This study explains additionally a behavior of metals such as nickel, magnesium, and iron during a carbonation of olivine bearing ore and leaching of a carbonated solid product.
Highlights
Olivine is a magnesium–iron silicate with the chemical formula (Mg, Fe)2 SiO4
In order to avoid a gel formation and to increase metal extraction a carbonation of olivine was performed at 175 °C and 71.5 bar carbon dioxide in water solution in the carbonation of20olivine was performed at 175 °C and 71.5 bar carbon dioxide in water solution in the presence of additives, producing amorphous silica (100–200 nm) and magnesium carbonate (2–5 μm)
In order to spare an added water (s/L: 0.1) enabling an enrichment of metals during new carbonation, obtained waste solution after filtration was again used in the autoclave, which is environmental friendly
Summary
Olivine is a magnesium–iron silicate with the chemical formula (Mg, Fe) SiO4. A distinction is made between magnesium olivine (Mg2 SiO4 ) with the name Forsterite and iron olivine (Fe2 SiO4 )Metals 2020, 10, 811; doi:10.3390/met10060811 www.mdpi.com/journal/metalsMetals 2020, 10, 811 with the name Fayalite. Olivine is a magnesium–iron silicate with the chemical formula (Mg, Fe) SiO4. A distinction is made between magnesium olivine (Mg2 SiO4 ) with the name Forsterite and iron olivine (Fe2 SiO4 ). Metals 2020, 10, 811 with the name Fayalite. Both types of olivine have a different degree of conversion for the maximum degree of carbonation. Olivine is formed deep in the upper mantle and occurs in mafic and ultramafic magmatic rocks [1,2]. Olivine can be described as a hexagonal dense spherical packing of oxygen atoms. Silicon is found in smaller tetrahedral gaps between four oxygen atoms
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