超声/磁场耦合作用下砷酸钠结晶热力学及动力学研究

Antimony storage of china is the first in the world. Sodium arsenate, easily soluble, is one of main substances from arsenic alkali residue, which will cause serious environmental pollution. There still exist many key engineering thermophysics problems during separation of sodium arsenate from mixture salts in crystallization by cooling, such as the absence of some important crystallization thermodynamics data for example metastable zone width, and indistinct mechanism of crystallization kinetics, as a result, it is difficult to control the crystallization processes and parameters and difficult to separate sodium arsenate from mixture salts. It is essential to research crystallization thermodynamics and kinetics of sodium arsenate, which will supply new approach to separate sodium arsenate. A novel technique is put forward in this project to separate sodium arsenate and other dissoluble sodium salts from arsenic alkali residue by coupling interaction of magnetic field and ultrasonics. The base crystallization thermodynamics of sodium arsenate will be determined using cool laser under coupling interaction of magnetic field and ultrasonics, and solid-liquid equilibrium phase diagram will be established. Crystallization thermodynamics of sodium arsenate by coupling interaction of magnetic field and ultrasonics will be researched to reveal particularity of crystal growth, size, and distribution in sollution. Experimental installation on the principle of coupling interaction of magnetic field and ultrasonics will be built, and control process to maintain crystalization and crystal growth of sodium arsenate will also be studied. Therefore, these can supply theoretic, thermodynamics and available approach of sodium arsenate separation from other dissoluble sodium salts, and may realize comprehensive utilization of arsenic alkali residue and can reduce environmental pollution.

我国锑资源拥有量为世界第一，易溶性砷酸钠是锑冶炼工艺中最严重污染物。现有常规砷酸钠冷却结晶工艺有诸多关键工程热物理问题尚未解决，如砷酸钠介稳区等重要结晶热力学数据缺乏、晶体析出及结晶动力学机制不清楚，导致结晶过程及参数难以控制、砷酸钠无法高效分离。因此开展较为系统的砷酸钠结晶过程热力学研究，从本质上认识结晶动力学机制，将为砷酸钠高效分离开辟新途径。本项目提出超声/磁场耦合技术诱导结晶分离砷酸钠。为此，采用冷激光测量砷酸钠溶液结晶过程重要热力学参数，建立砷酸钠的固液平衡相图；开展超声/磁场耦合作用下砷酸钠结晶动力学研究，揭示砷酸钠晶体生长、尺寸、晶体在结晶液中的分布等特殊规律；构建超声/磁场耦合作用下结晶分离的实验原理性装置，对维持砷酸钠分离结晶生长过程的条件进行控制。上述研究能为诱导砷酸钠高效分离提供有力的基础数据、热力学依据和有效的技术方法，从而实现砷碱渣的综合利用，减少环境污染。

我国锑资源拥有量为世界第一，易溶性砷酸钠是锑冶炼工艺中最严重污染物。现有常规砷酸钠冷却结晶工艺有诸多关键工程热物理问题尚未解决，如砷酸钠介稳区等重要结晶热力学数据缺乏、晶体析出及结晶动力学机制不清楚，导致结晶过程及参数难以控制、砷酸钠无法高效分离。为此，我们开展了较为系统的自然条件下和外场（超声场和磁场）条件下的砷酸钠结晶过程热力学研究，从本质上认识结晶动力学机制，为砷酸钠高效分离提供了有利的基础数据、热力学依据和有效的技术方法。.首先，我们分别研究了砷碱渣复合盐主要物质硫酸钠、砷酸钠在无外场、外加场条件下的结晶热力学和动力学，获得了一系列硫酸钠、砷酸钠的热力学和动力学数据，包括各种条件下的溶解度、超溶解度、介稳区、诱导期以及生长和成核动力学方程。发现超声会增大砷酸钠的溶解度，而磁场会减小其溶解度，二者都减小了砷酸钠的诱导期，加快了成核速率。砷酸钠的溶解度随着温度的升高不断增大的，砷酸钠的介稳区宽度随着温度的升高而变宽、诱导期随着过饱和度的增加而减小。由于二次成核的作用，晶体成核和生长达到了最大值，然后随着溶液中过饱和度减小，溶液中溶质分子的浓度降低，有序排列的几率降低，最终导致了成核和生长速率减小。.其次，研究了超声/磁场耦合条件砷酸钠的结晶热力学和动力学。结果表明在过饱和相同的条件下，超声提高了成核过程中的扩散系数，增加了成核的形成速率，降低了晶体的生长速度。同时超声能使介稳区宽度明显变窄，过饱和溶液变得更不稳定；而外加磁场降低了砷酸钠溶解度和介稳去宽度, 磁场大大增加了砷酸钠溶液的成核速率, 对砷酸钠的成核的促进作用更加明显，诱导期更短。研究还通过粒度分布、SEM、超景深显微，以及采用高超速摄像机对砷酸钠的结晶过程进行拍摄，从微观上表征砷酸钠晶体在各种条件下的成核及生长。.研究为诱导砷酸钠高效分离提供有力的基础数据、热力学依据和有效的技术方法。