Dissolution reactivity and kinetic model of low-grade limestone

doi:10.11949/0438-1157.20220864

Abstract

Abstract:

The non-creation and non-regeneration of limestone resources lead to the shortage of high-grade limestone and the continuous decline of limestone grades. The application of low-grade limestone leads to a decrease in the efficiency of the desulfurization system, which has gradually become a frequent accident in the industry. In order to study the dissolution kinetics of low-grade limestone in acidic environment, the effects of experimental variables including reaction temperature, slurry pH and initial particle size are investigated, respectively. The results show that the dolomite [CaMg(CO₃)₂] is the main impurity in low-grade limestone which has a much lower dissolution rate than that of CaCO₃ in acidic environment. The dissolution process of low-grade limestone is mainly controlled by the internal diffusion. In addition, a semi empirical dissolution kinetic equation of low-grade limestone is established based on the shrinkage model of unreacted core.

Key words: low-grade, dissolution, dolomite, internal diffusion control, kinetic

摘要：

石灰石资源的不可创造和不可再生导致优质石灰石资源逐渐稀缺，石灰石品位不断下降。低品位石灰石应用导致脱硫系统效率下降已逐渐成为行业内的频发事故。为明晰低品位石灰石脱硫浆液在酸性环境下的溶解动力学，开展了溶解体系温度、pH以及石灰石颗粒粒径等关键因素对低品位石灰石溶解特性的影响规律研究。结果表明，CaMg(CO₃)₂是低品位石灰石中存在的主要杂质，其在酸性环境中的溶解速率远低于CaCO₃；由CaMg(CO₃)₂形成的惰性残留层决定了低品位石灰石的溶解过程主要由产物层内扩散控制。此外，基于未反应核的收缩模型，建立了低品位石灰石的半经验溶解动力学方程。

关键词: 低品位, 溶解, 碳酸镁钙, 内扩散控制, 动力学

CLC Number:

TQ 028.8

Shuaiwei GU, Wei ZHANG, Zhen CHEN, Haiming WANG, Changfu YOU. Dissolution reactivity and kinetic model of low-grade limestone[J]. CIESC Journal, 2022, 73(12): 5547-5554.

顾帅威, 张纬, 陈阵, 王海名, 由长福. 低品位石灰石溶解特性及动力学模型[J]. 化工学报, 2022, 73(12): 5547-5554.

Figures/Tables 17

Table 1 Chemical components of low-grade limestone

元素	含量/%（质量）
Ca	34.44
Mg	3.5
Si	0.522
Al	0.133
Na	0.0858
Fe	0.0726

Fig.1 XRD patterns of low-grade limestone

Fig.2 Dissolution experimental setup

Table 2 Experimental conditions of low-grade limestone dissolution

实验	温度T/℃	pH	粒径d_p/μm
1	30	5.0	14.592
2	40	5.0	14.592
3	50	5.0	14.592
4	60	5.0	14.592
5	50	4.5	23.182
6	50	5.5	23.182
7	50	6.0	23.182
8	50	5.0	23.182
9	50	5.0	44.301
10	50	5.0	71.719

Fig.3 Conversion-time curves of low-grade limestone

Fig.4 XRD patterns of low-grade limestone dissolution products

Fig.5 SEM-EDS images of low-grade limestone dissolution under different conversion rates

Fig.6 Fitting analysis of low-grade limestone dissolution conversion rate with time at different reaction temperatures

Table 3 Dissolution rate constants of low-grade limestone at different temperatures

温度T/℃	溶解速率常数k/min^-1
30	0.001714
40	0.002679
50	0.003528
60	0.004532

Fig.7 Plot between lnk1 and 1/T

Fig.8 Fitting analysis of low-grade limestone (with different particle sizes) dissolution conversion rate with time

Table 4 Dissolution rate constants of low-grade limestone with different particle sizes

粒径d_p/μm	溶解速率常数k/min^-1
14.592	0.003528
23.182	0.002296
44.301	0.001176
71.719	0.0004885

Fig.9 Plot between ln(d[1+2(1-X) -3(1-X)2/3]/dt) and lndp

Fig.10 Fitting analysis of low-grade limestone (under different pH conditions) dissolution conversion rate with time

Table 5 Dissolution rate constants of low-grade limestones under different pH conditions

pH	H⁺浓度c_A/(mol/L)	溶解速率常数k/min^-1
4.5	10^-4.5	0.003700
5.0	10^-5.0	0.002296
5.5	10^-5.5	0.001116
6.0	10^-6.0	0.0004514

Fig.11 Plot between ln(d[1+2(1-X) -3(1-X)2/3]/dt) and lncA

Fig.12 Plot between 1+2(1-X) -3(1-X)2/3 and dp-1.213cA0.6108exp(-26900/RT)t

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