Process for treatment of pyrochlore concentrates

A continuous process for treatment of niobium ore concentrates containing titanium, rare earth, thorium, iron and alkaline earth in addition to niobium to extract niobium, rare earths and thorium, comprising the steps of:

• 1. digesting the ore with a hot solution containing 13 to 16 moles of sulphuric acid per liter;
• 2. diluting the solution with aqueous medium to a concentration of 10.5 to 13 moles of sulphuric acid per liter to precipitate iron, alkaline earth and some of the rare earths as their sulphates;
• 3. separating the undigested residue and the precipitated sulphates from the solution;
• 4. reducing titanium in the solution from the tetravalent state to the trivalent state;
• 5. diluting the solution with aqueous medium to a concentration of 4 to 7 moles of sulphuric acid per liter to precipitate niobium oxide, and thorium and the remainder of the rare earths as their sulphates, leaving the tetravalent titanium in solution;
• and
• 6. separating the precipitate consisting essentially of niobium oxide and sulphates of thorium and rare earths.