Chemically removing iron from grits

Claim 1

In a process of removing iron from grits of brown or white corundum, silicon carbide, zirconium corundum or garnet having a Mohs hardness of 7 to 9, with hydrochloric acid wherein: (a) a mixture of the grits and aqueous hydrochloric acid is agitated for removal of the iron from the grits and the provision of a first suspension of the grits in an aqueous hydrochloric acid medium in which the iron is dissolved, and the aqueous hydrochloric acid medium is removed from the grits, the improvement which comprises passing the grits serially through at least two hydrocyclones having no moving parts, adding water to the feed to each hydrocyclone, and in each hydrocyclone separating aqueous hydrochloric acid and forming a specifically heavier fraction containing the grits, (b) for the first hydrocyclone separation, adding water to said first suspension to form a second suspension and feeding the second suspension tangentially into the first hydrocyclone for centrifuging the second suspension in the first hydrocyclone and thereby separating therefrom a specifically lighter fraction rich in the hydrochloric acid and a first specifically heavier fraction rich in grits, the first specifically heavier fraction being removed from the bottom of the hydrocyclone, (c) for the second hydrocyclone treatment, adding water to said first specifically heavier fraction to form a third suspension and feeding the third suspension tangentially into a second hydrocyclone for centrifuging the third suspension in the second hydrocyclone and thereby separating the third suspension into a second specifically lighter fraction rich in hydrochloric acid and a second specifically heavier acid-free fraction rich in grits, the second specifically heavier acid-free fraction being removed from the bottom of the second hydrocyclone, and (d) the specifically heavier fraction produced in last hydrocyclone is filtered for preliminary dewatering to provide a filter cake containing the grits and the filter cake is dried to provide dried grits substantially free of iron, (e) said first suspension is continuously supplied to step (b) and the subsequent steps are performed continuously.