A Spectroscopic Study On The Decomposition Of Magnesium Silicate By Alkali Fusion Using NaOH

The demand of nickel has increased over time and is correlated with economic development. Normally, the demand for stainless steels and other alloys are driving demand for nickel. Now the majority of nickel has been produced from sulfide nickel ores although this is changing owing to the lack of the sulfide ores. The nickel silicate, primarily serpentine, although which contains less 2wt% nickel, has been used as raw material for production of nickel. Several new technologies are developed for extraction of nickel in the environmental sound manner from the silicate ores with the higher chemical and thermal stability, including the joint process of alkali-roasting activation and acid-leaching. Here, the mechanism of alkali activation for the silicate, especially on the pathway of the reactions was studied in detail, which results should be significant to understand and optimize the process.MgSiO3 was prepared by the chemical precipitation method from analytical grade MgCl2 and Na2SiO3 in the aqueous solution. Mg2SiO4 and MgNiSiO4 were synthesized by the solid reaction of MgSiO3 prepared in this study and analytical grade MgO or NiO at 1200℃, respectively. Here, we used the synthetic MgSiO3, Mg2SiO4 and MgNiSiO4 instead of the natural garnierite, and reveal the reaction pathway to the alkali fusion by spectroscopic methods. The main results are summarized as following.Combining Raman spectroscopy in situ with the XRD and IR analyses can give the reaction pathway for the decomposition of MgSiO3, Mg2SiO4 and MgNiSiO4 during the alkali fusion process using NaOH. The silica tetrahedral chains within magnesium inosilicate (MgSiO3) is gradually disrupted, and nesosilicate with the isolated tetrahedral reorganized since the beginning of the alkali fusion process. Mg2SiO4 and Na2MgSiO4 are the two intermediates for the decomposition while final products are Mg(OH)2 and Na4SiO4. It can be deduced that this decomposition could not initiate from the cation exchange reaction. The alkali fusion of Mg2SiO4 and MgNiSiO4 with the island structure was broken down the bonds by NaOH. The Mg ions and Ni ions were substituted by the sodium atoms, and it can significantly improve the course of the alkali fusion process by extending the reaction time, the reaction temperature and increasing the amount of alkali.In the alkali fusion process, the reaction radio of the base material, the reaction time and the reaction temperature can be increased to improve the dissolution rate of silicon, wherein the base material is the decisive role. When the base material is relatively low, the dissolution rate of silicon significantly increased with the reaction time and the reaction temperature improving. When the base material is relatively high, the reaction tends to be balanced quickly.