Some embodiments of the present invention relate to a method for reducing the concentration of reactive silica in a first composition comprising adding a first amount of a calcium salt and a second amount of a magnesium salt to the first composition to form a solid silicate composition comprising one or more silicates, wherein the first composition comprises an aqueous solution; and a significant portion of the reactive silica in the first composition is converted to one or more silicate in the solid silicate composition.

Some embodiments of the present invention relate to a method for reducing the concentration of reactive silica in a first composition comprising adding a first amount of a calcium salt and a second amount of a magnesium salt to the first composition to form a solid silicate composition comprising one or more silicates, wherein the first composition comprises an aqueous solution; and a significant portion of the reactive silica in the first composition is converted to one or more silicate in the solid silicate composition.

A method for reducing or preventing corrosion or fouling in an apparatus for carrying out a chemical process, where corrosion or fouling is caused by acidic compounds present in the chemical process, which comprises the addition of at least one quaternary ammonium hydroxide of the formula (I) to the apparatus, wherein the chemical process is carried out: [Chem. 1] where R.sup.1, R.sup.2, R.sup.3 are each independently C.sub.1-C.sub.10 alkyl; R.sup.4 is inter alia C.sub.1-C.sub.18 alkyl, benzyl, monocycloalkyl having 5, 6, 7 or 8 carbon atoms, bicycloalkyl having 6 to 8 carbon atoms, tricycloalkyl having 7 to 10 carbon atoms, where monocycloalkyl, bicycloalkyl and tricycloalkyl are unsubstituted or substituted by 1 or 2 methyl groups, or tri-C.sub.1-C.sub.4 alkyl ammonium groups. R.sup.1 and R.sup.2 together with the nitrogen atom may also form a 5 or 6-membered, saturated nitrogen heterocycle, which is unsubstituted or carries 1 or 2 methyl groups; and/or R.sup.3 and R.sup.4 together with the nitrogen atom may also form a 5 or 6-membered, saturated nitrogen heterocycle, which is unsubstituted or carries 1 or 2 methyl groups.

A method for reducing or preventing corrosion or fouling in an apparatus for carrying out a chemical process, where corrosion or fouling is caused by acidic compounds present in the chemical process, which comprises the addition of at least one quaternary ammonium hydroxide of the formula (I) to the apparatus, wherein the chemical process is carried out: [Chem. 1] where R.sup.1, R.sup.2, R.sup.3 are each independently C.sub.1-C.sub.10 alkyl; R.sup.4 is inter alia C.sub.1-C.sub.18 alkyl, benzyl, monocycloalkyl having 5, 6, 7 or 8 carbon atoms, bicycloalkyl having 6 to 8 carbon atoms, tricycloalkyl having 7 to 10 carbon atoms, where monocycloalkyl, bicycloalkyl and tricycloalkyl are unsubstituted or substituted by 1 or 2 methyl groups, or tri-C.sub.1-C.sub.4 alkyl ammonium groups. R.sup.1 and R.sup.2 together with the nitrogen atom may also form a 5 or 6-membered, saturated nitrogen heterocycle, which is unsubstituted or carries 1 or 2 methyl groups; and/or R.sup.3 and R.sup.4 together with the nitrogen atom may also form a 5 or 6-membered, saturated nitrogen heterocycle, which is unsubstituted or carries 1 or 2 methyl groups.