Na[Al(OH)4] + 3NaOH + 3H2O Na4[Al(OH)7]•3H2O
Sodium tetrahydroxoaluminate react with sodium hydroxide and water to produce trihydrate heptahydroxosodium aluminate. Tetrahydroxoaluminate - saturated solution. Sodium hydroxide - 50% solution. This reaction takes place at a temperature of 60-65°C.