The alkali agents include hydroxides such as sodium hydroxide, potassium hydroxide and calcium hydroxide, carbonates such as sodium carbonate, potassium carbonate and sodium sesquicarbonate (sodium monohydrogen-dicarbonate), silicates such as sodium silicate and potassium silicate, alkanolamines such as monoethanolamine, diethanolamine, triethanolamine and 2-amino-2-methyl-1-propanol, as well as <