Characterization and dissolution of scale formed during continuous pressure acid leaching of laterites.

摘要

The focus of this work was the study of scale produced as a by-product from the Falconbridge laterite pressure acid leaching campaigns conducted during the period 2000 to 2002. The objective was twofold: (i) scale characterization, (ii) scale dissolution.; The results obtained from the scale characterization studies revealed that alunite formed in fresh water and saline water had the general chemical formula of (H3O)Al3(SO4)2(OH) 6 (hydronium alunite) and NaAl2Fe(SO4)2(OH) 6 (sodium alunite), respectively. In saline water campaigns, Fe substitutes Al within the alunite structure---compared to that of pure hydronium alunite---at an average Al:Fe molar ratio of 2:1. Alunite comprises 67 wt% of the scale mass with hematite, making up the balance.; The scale growth rates were found to be highest at the compartment of acid addition. Those obtained from the saline water campaigns were 200% greater than fresh water campaigns.; The scale dissolution tests examined the effectiveness of chemicals dissolving scale as a measure of descaling. Two scales were tested, I3 and I6. Maximum dissolution was attained with HCl, instead of H2SO 4 at the most vigorous conditions of 200°C and 0.5m. Also, the dissolution kinetics of I3 were twice as fast as those of I6 due to the five-fold porosity of the former scale.