Hydrothermal decomposition of potassium feldspar under alkaline conditions

Abstract

For the first time, a transitional compound [Ca2+ ≡ 2AlSi3O8− ≡ xOH−] was observed for K-feldspar hydrothermal alkaline decomposition, and a model was presented.

Study of K‐Feldspar and Lime Hydrothermal Reaction at 190 °C: Phase, Kinetics and Mechanism with Reaction Time

“…However, Tm–2 contained a higher content of amorphous phases than Tm‐1, showing that some phases unidentified by XRPD were formed for Tm–2 at 190 °C due to its higher percentage of dissolution. These amorphous compounds may be calcium silicate hydrates or some transition state compounds that were found in previous work . For brevity, we called these compounds amorphous calcium silicate hydrate (ACSH) and did not further investigate them.…”

“…Several researchers also studied the preparation of potassium fertilizer via the hydrothermal alternation of K‐feldspar ore at 200 °C . Additionally, we studied the hydrothermal dissolution mechanism of K‐feldspar and lime through a solid‐liquid interface and found that the dissolution was due to mineral‐mineral replacement reactions that occurred by the dissolution‐precipitation mechanism . However, none of the abovementioned studies investigated the hydrothermal reaction of K‐feldspar under alkaline conditions with various reaction times.…”

“…For Tm–3, we can see that many slices appeared on the unreacted K‐feldspar particles. Spherical particles are observed in the images of Tm–4 to Tm–10, and these spherical particles were grossular, as identified in our previous study and by other researchers ,, . Rod‐like or needle‐like particles were found in the images of Tm–6 to Tm–10, and these particles were considered to be tobermorite, as identified in our previous study and by other researchers ,, , .…”

“…Spherical particles are observed in the images of Tm–4 to Tm–10, and these spherical particles were grossular, as identified in our previous study and by other researchers ,, . Rod‐like or needle‐like particles were found in the images of Tm–6 to Tm–10, and these particles were considered to be tobermorite, as identified in our previous study and by other researchers ,, , . With prolonged time, the formed phases were deposited on the surface of K‐feldspar and intertwined with each other.…”

“…Both potassium carbonate and bütschliite originated from potassium hydroxide, which is one of the primary products of the hydrothermal reaction. The remaining released K was from water‐insoluble product, namely, the difference between the results obtained with 0.5 mol L −1 HCl and those obtained with deionized water (Table S1) may be due to the structure of tobermorite because EDS data suggested that tobermorite contained some K atoms in our previous study, and several K ions entered into tobermorite to maintain electrical neutrality for the Al‐substituted tobermorite …”