Solid-liquid chaotic mixing and leaching enhancement performance in phosphoric acid leaching process

doi:10.11949/j.issn.0438-1157.20181253

Abstract

Abstract:

In the process of wet-process phosphoric acid leaching, the mode of action of the traditional rigid stirring paddle is mainly shearing, and it is easy to form a symmetrical flow field structure and reduce the stirring efficiency. The effects of impeller type, impeller off-bottom clearance, stirring speed, length of flexible wire, diameter of flexible wire on leaching rate and largest Lyapunov exponent (LLE) were investigated experimentally. The results showed that rigid-flexible impeller changed structure of flow field and improved the fluid chaos mixing degree through coupling interaction of rigid-flexible-fluid. At leaching time 120 min, agitation speed 225 r/min, off-bottom clearance h=T/4, diameter of wire d=0.42r and length of wire L=1.3T, LLE of rigid-flexible impeller reached 0.9071 and leaching rate of phosphate rock increased by 10.8%. At the same power consumption (P _v=9860 W/m³), the suspension uniformity and the slag phosphorus content were reduced by 40.8% and 17.67% with the rigid-flexible impeller, respectively. In addition, the morphology of the crystal was improved when the rigid-flexible impeller was used. Meanwhile, the filtration performance of phosphogypsum was enhanced.

Key words: wet-process phosphoric acid, rigid-flexible impeller, two-phase flow, leaching, crystallization, largest Lyapunov exponent

摘要：

湿法磷酸浸出过程中，传统刚性搅拌桨的作用方式主要是剪切作用，容易形成对称性流场结构，降低搅拌效率。实验考察了桨叶类型、离底高度、搅拌速度、柔性钢丝绳长度、柔性钢丝直径对磷矿浸出率及最大Lyapunov指数(LLE)的影响。实验结果表明：刚柔组合桨通过刚-柔-流的耦合作用，改善流场的结构，提高了流体混沌混合效果。当搅拌转速225 r/min，浸出时间120 min，离底高度h=T/4，柔性钢丝绳直径d= 0.42r，柔性钢丝绳长度L=1.3T时，刚柔组合桨的最大Lyapunov指数达到0.09071，磷矿浸出率提高了10.8%。另外，在相同的功耗(P _v=9890 W/m³)条件下，刚柔组合桨使反应器内的悬浮均匀度和渣中磷含量分别降低了40.8%和17.67%，有效地改善了晶体的形貌，提高了磷石膏的过滤性能，强化了颗粒的混合与浸出。

关键词: 湿法磷酸, 刚柔组合桨, 两相流, 浸取, 结晶, 最大Lyapunov指数

CLC Number:

TQ 027.2

Bing LI, Yi YANG, Zuohua LIU, Changyuan TAO, Deyin GU, Chuanlin XU, Yundong WANG. Solid-liquid chaotic mixing and leaching enhancement performance in phosphoric acid leaching process[J]. CIESC Journal, 2019, 70(5): 1742-1749.

李兵, 杨义, 刘作华, 陶长元, 谷德银, 许传林, 王运东. 湿法磷酸固-液体系混沌混合与浸出强化行为[J]. 化工学报, 2019, 70(5): 1742-1749.

Figures/Tables 18

Fig.1 Experimental setup

Fig.2 Schematic diagram of impeller

Fig.3 XRD pattern of phosphate

Fig.4 Effect of impeller type on leaching rate

Fig.5 Effect of impeller type on LLE

Fig.6 Effect of different speed on leaching rate

Fig.7 Effect of impeller off-bottom clearance on leaching rate

Fig.8 Effect of impeller off-bottom clearance on LLE

Fig.9 Effect of diameter of flexible wire on leaching rate

Fig.10 Effect of diameter of flexible wire on LLE

Fig.11 Effect of length of flexible wire on leaching rate

Fig.12 Effect of length of flexible wire on LLE

Fig.13 Effect of impeller type on suspension uniformity

Fig.14 Effect of impeller type on power consumption

Fig.15 Effect of impeller type on residual phosphorus

Fig.16 Filtering effect(a)/permeability(b) change with time

Fig.17 SEM images of phosphogypsumr

Fig.18 XRD patterns comparison of slag

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