Study of K-Feldspar and Lime Hydrothermal Reaction: Phase and Mechanism with Reaction Temperature and Increasing Ca/Si Ratio

Shanke Liu,Cheng Han,Jianming Liu

doi:10.3390/min9010046

Abstract

To elucidate the physicochemical properties of the artificial silicate composite material, K-feldspar and lime were reacted in mild hydrothermal conditions (different reaction temperatures and various K-feldspar/lime ratios). Formed phases were investigated using various techniques, such as X-ray powder diffraction, the Rietveld method, scanning electron microscopy (SEM), and inductively coupled plasma-optical emission spectrometry. The analysis revealed that tobermorite, grossular (hydrogarnet), alpha-dicalcium silicate hydrate (α-C2SH), amorphous calcium silicate hydrate, potassium carbonate, bütschliite, calcite, and calcium hydroxide formed with various conditions. Both the temperature and the Ca/Si molar ratio in the starting material greatly affected the formation of phases, especially the generation of tobermorite and α-C2SH. The substitution of H4O4 ↔ SiO4 proceeded with the increase of the Ca/Si molar ratio rather than the reaction temperature and the reaction time. More hydrogen was incorporated in hydrogarnet through the substitution of H4O4 ↔ SiO4 with the increase of the Ca/Si molar ratio in the starting material. Due to the properties of tobermorite as a cation exchanger and its potential applications in hazardous waste disposal, experimental parameters should be optimized to obtain better performance of the artificial silicate composite material from K-feldspar and lime hydrothermal reaction. The dissolution mechanism of K-feldspar was also discussed.

Highlights

Silicates are extremely important materials, both naturally and artificially, for the development of science and technology
We only show new analysis and supply additional data to better understand the physicochemical properties of K-feldspar and lime hydrothermal reactions
Based on an environmentally friendly hydrothermal process, the artificial silicate composite material generated from natural silicate rock, i.e., K-feldspar, exhibited complex mineralogical properties

Summary

Introduction

Silicates are extremely important materials, both naturally and artificially, for the development of science and technology. An artificial silicate composite material, namely a nanosubmicron mineral-based soil conditioner (NMSC) prepared by the hydrothermal reaction of K-feldspar and lime, was reported [5,6,7]. Field and in-house tests indicated that the artificial silicate composite material showed excellent performance and served multiple functions that were closely related to its physicochemical properties and mineral components [8,9]. Of them, both carbonates and 11 Å tobermorite contributed to pH improvement and the inhibition of cadmium (Cd) uptake in rice.

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Conclusion