digestion

Although monazite is very stable chemically, it is susceptible to attack by both strong mineral acids (e.g., sulfuric acid, H₂SO₄) and alkalies (e.g., sodium hydroxide, NaOH). In the acid treatment, finely ground monazite sand is digested at 155 to 230 °C (310 to 445…

…it is pumped to the digester at the start of a “cook,” consists of free sulfur dioxide dissolved in water at a concentration of 4 to 8 percent, together with from 2 to 3 percent in the form of bisulfite. Sulfite digestion is normally carried out as a batch process…