Interaction between Tuff and Calcium Hydroxide under Hydrothermal Conditions for Obtaining a Potash Fertilizer
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NOLOGY OF INORGANIC SUBSTANCES AND MATERIALS
Interaction between Tuff and Calcium Hydroxide under Hydrothermal Conditions for Obtaining a Potash Fertilizer K. G. Grigoryana, L. G. Baginovaa, A. A. Khachatryana, *, S. M. Ayrapetyana, G. A. Arutyunyana, A. K. Kostanyana, and A. N. Aznauryana aManvelyan
Institute of General and Inorganic Chemistry, National Academy of Sciences of the Republic of Armenia, Yerevan, 375051 Armenia *e-mail: [email protected] Received September 1, 2017; revised February 5, 2018; accepted February 28, 2018
Abstract—The interaction between dacitic tuff and calcium hydroxide under hydrothermal conditions has been investigated. At a ratio of CaO/SiO2 = 0.3–1.5 : 1 and at a ratio between the liquid phase and the solid phase amounting to 10 : 1, after 2 h at 220°C, calcium hydroxide is completely bound. As a result of the destruction of potassium feldspar in tuff, potassium can be transformed into a plant-digestible form. Keywords: dacitic tuff, calcium hydroxide, hydrothermal conditions, potash fertilizer DOI: 10.1134/S0040579519050075
INTRODUCTION In the territory of Armenia, there are reserves of alkali aluminosilicates with a high content of potassium. Among these rocks, dacitic tuffs are of particular interest for the production of potassium-containing fertilizers. The main rock-forming components of tuffs are represented by potash feldspar (orthoclase) (KAlSi3O8 in an amount ranging from 58.0 to 78.0 wt %) and quartz. Components such as plagioclase, mica minerals, calcite, magnetite, etc., occur as well [1]. These rocks are characterized by a negligible content of sodium. The molar ratio between K2O and Na2O amounts to 20–40 : 1, whereas other alkaline aluminosilicates are characterized by a ratio of 1.4– 1.8 : 1 [1]. Taking into account the potentialities of obtaining potash fertilizers from these rocks, the factor of low sodium content could play a favorable role for agricultural purposes. As far as complex rock processing is concerned, such rocks are not of practical interest, owing to the fact there are not many reserves of these rocks [2]. The potassium contained in feldspar is inaccessible to plants. To convert potassium into a form appropriate for assimilation by plants, a technology is required that can provide the feldspar framework structure to destruct. Earlier, the authors performed studies concerning a technique that makes it possible to activate the feldspar by means of tuff roasting with CaO and CaCО3 for the partial disruption of its framework lattice, and
thus convert K2O into a digestible form to obtain a slow-acting fertilizer [3]. In [4] there are indications that the formation of alkali hydroaluminosilicates such as potassium analcime is possible under the conditions of hydrothermal synthesis involving orthoclase and Ca(OH)2, according to the following equation:
K 2O ⋅ Al 2O3 ⋅ 6SiO2 + 2Ca(OH)2 + 3H2O = K 2O ⋅ Al 2O3 ⋅ 4SiO2 ⋅ H2O + 2(CaO ⋅ SiO2 ⋅ 2H2O) or the formation of potassium natrolite is possible according to the following equation:
K 2O ⋅ Al 2O3 ⋅ 3
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