Leaching kinetics of impurity removal from aphanitic graphite by HCl leaching

As a systematic study, this investigation explored the effects of various leaching conditions (hydrochloric (HCl) acid concentration, solid-liquid ratio, temperature, reaction time, and stirring speed on graphite impurity removal rate) to model the ash removal leaching kinetics and evaluated their mechanisms by analytical analyses. The single-factor results indicated that the optimal impurity removal rate (alpha) was 14.64% at 8 mol/L HCl concentration, 0.1 g/mL solid-liquid ratio, 343 K acid leaching temperature, 120 min reaction time, and 400 rpm stirring speed. Iron-bearing minerals were efferently removed using HCl. The kinetic process analyses indicated that the aphanitic graphite acid leaching process for the ore fitted well with the unreacted shrinkage core model (diffusion reaction). The reaction's apparent activation energy (E-a) was 23.43 kJ/mol, and the leaching process's frequency factor (A) was 15.17. The kinetic equation could be considered as (1 - 3(1-alpha))(2/3)+2(1-alpha) = 15.17e(-23.43/(RT))t. From the results, it was concluded that the HCl acid leaching process belongs to diffusion control.