Very often smectite clays, such as montmoriionite clays, are formed naturally by the alteration of volcanic glass (sodium, magnesium aluminosilicate) under hydrothermal conditions (heat and pressure). The average crystal-chemical formula for montmorillonite is E.sub.0.33 (Al.sub.1.67 Mg.sub.0.33)Si.sub.4 O.sub.10 (OH).sub.2 .cndot.nH.sub.2 O, wherein E=Na, Ca, and/or Mg and n=1-80. Almost all montmorillonite deposits include non-montmorillonite mineralogical phases, such as quartz (crystalline silica) or amorphous silica contaminants, commonly in amounts of about 10% by weight to as much as about 50% by weight. Prior art techniques for removal of silica contaminants include removing the silica by solubilizing the silica at high pH and separating the solid montmorillonite clay in a more pure form. The removal of such contaminants is a time consuming and expensive process and results in wasting the SiO.sub.2 portion of the starting material.
In accordance with the present invention, a method has been found to convert the silica fraction of a recovered montmorillonite clay/silica deposit to a dioctahedral smectite clay, such as a montmorillonite clay, or to a trioctahedral smectite clay, such as hectorite, thereby obtaining a relatively pure dioctahedral and/or trioctahedral smectite clay without wasting the silica impurities recovered with the clay deposit.
While others have synthesized smectites or montmorillonites from sodium, magnesium aluminosilicate glass in a hydrothermal process, "Montmorillonite Crystallization From Glass", Nakazawa, et al., Clay Science, 8, 59-68(1991), and at atmospheric pressure and low temperature, "Synthesis Of Smectite From Volcanic Glass At Low Temperature", Tomita, et al., Clays and Clay Minerals, Vol. 41, No. 6, 655-661(1993), these synthesis reactions are reactions of a glass material (recovered volcanic glass material, or glass material prepared by fusion of a mixture of oxides and carbonates, e.g., SiO.sub.2, Al.sub.2 O.sub.3, MgO, and Na.sub.2 CO.sub.3) with water at various NaOH concentrations, and required 3 to 7 days for hydration of the starting materials, without the addition of metal ions.
In accordance with one embodiment of the present invention, SiO.sub.2 is converted to essentially pure dioctahedral smectite clay, containing less than about 5% by weight non-clay impurities, preferably less than about 2% by weight non-clay impurities, more preferably less than about 1% by weight non-clay impurities, e.g., to montmorillonite, beidellite and/or nontronite. The SiO.sub.2 is altered to the structure of a dioctahedral smectite clay, preferably montmorillonite, by the addition of Al, Mg and/or Na ions to convert crystalline silica and/or amorphous silica to a dioctahedral smectite clay, such as a montmorillonite.
In accordance with another embodiment of the present invention, SiO.sub.2 is converted to essentially pure trioctahedral clay, such as hectorite, containing less than about 5% by weight non-clay impurities, preferably less than about 2% by weight non-clay impurities, more preferably less than about 1% by weight non-clay impurities. The SiO.sub.2 is altered to the structure of a trioctahedral clay, preferably hectorite, by the addition of Li, Mg and/or Na ions to convert crystalline silica and/or amorphous silica to a trioctahedral smectite clay, such as hectorite.