Dissolution rates of jarosite-type compounds in H2SO4 medium: A kinetic analysis and its importance on the recovery of metal values from hydrometallurgical wastes

- It was performed a kinetic study on the dissolution of M-As jarosites (M = Na, K, NH4) in H2SO4 medium.
- Temperature is the variable that presented the strongest effect on the dissolution rate.
- The substituent in the M-site has no effect on the dissolution rates in acid medium.
- Results of n and Ea confirm that extreme T and pH conditions are necessary to obtain high dissolution rates.
- It is proposed a kinetic model that describes the dissolution process of jarosite-type compounds in acid medium.

This investigation reports the dissolution kinetics of Na-As, K-As and NH4-As jarosites in a sulfuric acid medium. The effects of the pH, temperature (T), particle size (d0), and structure substituents (especially in the M and Z positions of the general formula of jarosite-type compounds, MFe3(ZO4)(OH)6) were investigated. The experimental results demonstrate that the temperature is the variable with the most significant effect on the dissolution rate, followed by the pH and particle size. In addition, it was observed that the type of substituent does not affect the dissolution rates in the acid medium. These results are reasonably consistent with the shrinking core model of chemical control for the dissolution of jarosite-type compounds under extreme pH conditions (≤ 1.0) and control by mass transfer at intermediate pH conditions (> 1.0). The results obtained were compared with those of other investigations, and it was observed that the dissolution of jarosite-type compounds could have important implications on the recovery of metal values. Finally, a kinetic model is proposed to describe the dissolution process of jarosite-type compounds in the acid medium.