A Study On The Pretreatment Process For The Rare Earth Ore Separation Wastewater

The study was focused on how to avoid the impediment of hardness during the treatment of the rare earth separation wastewater.First of all, the character of the pollution in the wastewater was analyzed. Then the reason for the impediment of hardness in the wastewater was studied by experiment. The results showed that: because of the NH₄⁺ and salt effect Mg²⁺ and OH^- together with Ca²⁺ and SO₄^2- could exist. After the NH₄⁺ was removed by the steam stripping process, the balance would be destroied. So, the precipitation came out.The technics for the treatment of the wastewater with high ammonia nitrogen and the wastewater with high hardness was studied. The chemical precipitation could be used for the removal of ammonia nitrogen and the reduction of hardness simultaneously; the precipitate was one of the wonderful composite fertilizers as well. So, it was investigated as a pre-treating technics.The results of the chemical precipitation showed that: pH and the proportion of the ions were the most important factors for the experiment. When pH = 9.0 and n(Mg²⁺):n(PO₄^3-)= 1:0.975, the content of PO₄^3- in the wastewater was only 4.9mg/L; the content of hardness in the wastewater was reduced from 9000mg/L to 528mg/L whose removal rate was 94.1%.The performance of the chemical precipitation was verified with the homemade stripping tower. The results showed that: with the help of the chemical precipitation hardness in the wastewater was reduced to a low level; the carbonate scaling problems of the stripping tower and the pipes were solved well; the system went on the rails.All these gave new ways for the treatment of the rare earth separation wastewater which were high in ammonia nitrogen and hardness. And they were helpful for the relative study in future as well.