Leaching kinetics of impurity removal from aphanitic graphite by HCl leaching

ABSTRACT

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 (α) 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−α))^2/3+2(1−α) = 15.17e^{–23.43/(RT)}t. From the results, it was concluded that the HCl acid leaching process belongs to diffusion control.

KEYWORDS:

• Aphanitic graphite
• HC leaching
• purification
• leaching kinetics

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

Yupeng Liu: conceptualization, investigation, writing-original draft preparation; Zheng Tong: methodology, software, validation, formal analysis, investigation; Mengqian Ni: methodology, software; Xibing Ren: validation, formal analysis; Xiangning Bu: supervision, conceptualization, methodology, investigation, review and editing, resources; Huaizhi Shao: supervision, writing-review and editing, visualization; S. Chehreh Chelgani: writing-original draft preparation, investigation, review and editing, visualization, supervision.

Novelty statement

Although many studies have focused on conventional leaching of graphite ore, there is considerable lack of information concerning thermodynamic modeling of aphanitic graphite acid leaching in the literature. To cover this knowledge gap, the current study aims to determine the thermodynamic parameters of the aphanitic graphite leaching process based on the Arrhenius formula.

Some findings are given as follows:

(1) 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−α))^2/3+2(1−α) = 15.17e^{–23.43/(RT)}t.

(2) Hydrochloric acid could remove Clinochlore. Silica-containing minerals (Quartz and chlorite-serpentine) are difficult to remove by hydrochloric acid.

Additional information

Funding

The work was supported by the National Natural Science Foundation of China [52204296]