硫酸铝高效浸取离子吸附型稀土和尾矿污染物控制技术的机理和性能

Ion adsorbed rare earth is a kind of very important strategic resource. Aiming at the problems of low leaching efficiency, large waste water emission and high risk of tailing landslide, aluminum sulfate is selected as leaching agent to improve the leaching efficiency, to reduce waste water discharge and prevent landslides. Meanwhile, magnetic resonance imaging (MRI) is firstly introduced to trace the water molecule coordinated to rare earth ions during the column leaching.Therefore, the zeta potential and water proton magnetic resonance imaging efficiency of the rare earth ions adsorbed clay minerals will be measured and correlated with the leaching rate of rare earths. Based on the electric double layer model and ion hydration theory, the forms of rare earth and aluminum ions adsorbed on clay minerals were evaluated with respect to the interaction between clay mineral and electrolyte solutions. A new mechanism of ion exchange or migration during the leaching process of rare earth with aluminium ion is put forward to explain the influencing factors on leaching efficiency, to evaluate the contribution of aluminum sulfate for improving the leaching rate of rare earths, and to determine the optimum leaching conditions of processes. With the measured ion concentration in leaching solution and zeta potential of clay mineral particles in the process of leaching and the subsequent rising process with water and lime water, the concrete behavior of aluminum in tailing and its contribution in reducing waste water discharge and preventing landslide risk are evaluated based on the isotherm equation of clay mineral particles for adsorbing rare earth, aluminum and magnesium ions. Furthermore, the characteristics and advantages of leaching rare earths with aluminum sulfate are revealed, and a new process for high efficiency green extraction of ion adsorption rare earth will be proposed.

离子吸附型稀土是一类非常重要的战略资源。本项目针对该类资源开采效率低，废水量大和尾矿塌方滑坡风险高等问题，拟用硫酸铝作浸取剂来提高收率、减少废水排放并防止滑坡，同时将磁共振造影方法引入柱上淋洗过程中水和稀土离子的造影跟踪。为此，测定黏土矿物吸附稀土和交换浸出过程的zeta电位和水质子磁共振造影效率并与稀土浸取率相关联；以双电层模型和离子水化理论为基础，研究电解质溶液与黏土矿物的相互作用，评价稀土和铝离子的存在形式及其在浸取、迁移过程中的变化，提出新的稀土离子交换浸出机理来说明影响浸取效率的各种因素，评价硫酸铝对提高稀土浸取率的贡献程度，确定最优化的浸取工艺和条件；基于黏土矿物粒子吸附稀土、铝和镁等离子的等温线方程，根据在浸取和后续水浸洗、石灰水护尾过程中黏土矿物的zeta电位和溶浸液中离子浓度，评价尾矿中铝的具体行为及其在控制污染物排放，防止尾矿滑坡中的贡献，提出高效绿色提取新流程。

离子吸附型稀土是一类非常重要的战略资源，但其开采存在效率低，废水量大和尾矿滑坡风险高等重大问题，急需通过揭示稀土浸取和污染物产生的机理，提出新的高效绿色浸取工艺。为此，本项目首先采用我们新建立的连续滴定法研究了电解质阴阳离子种类和浓度在浸取离子吸附型稀土时粘土粒子zeta电位、悬浮液pH和电导以及稀土浸取效率等基本特征的变化规律及其相互关系。利用每一电解质的稀土浸出浓度和zeta电位的线性关系斜率来比较浸取能力，证明硝酸盐浸取稀土和氢离子的能力以及尾矿粘土粒子zeta电位的变化次序均为铝>钙~镁~锌>钾>铵>钠，与它们的离子势大小次序相符；而在硫酸介质中，浸取率次序为铝>钾>铵>镁~锌>钠，钾铵的浸取能力前移并超过两价离子，这与硫酸根的配位吸附相关。采用柱上淋洗、静态吸附和低场磁共振方法也得到类似的变化规律。根据离子水化理论和双电层模型，认为稀土浸取率主要取决于浸取剂水合阳离子的离子势和阴离子的配位吸附等热力学因素，而离子迁移等动力学条件的影响也能起到调谐作用。要实现高效浸取，需要选择离子势强的离子，例如铝等。它们被粘土表面吸附而进入水膜紧密层，将稀土和其他离子交换浸出，导致zeta电位反转。而硫酸根的配位吸附能调谐zeta电位到零，并使稀土配位后的离子势降低而被浸出。低价离子被粘土吸附进入紧密层的驱动力不足, 对稀土的浸取需要依靠zeta电位负值增大来改善离子迁移的动力学条件，但也伴随着水土流失的发生。因此，单独选择硫酸铝作浸取剂，虽然浸取效率最高，滑坡风险最低，但由于尾矿zeta电位接近于零，离子迁移的动力学受到影响，浸出液中铝的分离压力大。为此，我们基于铝与镁、钠、钾、钙等低价离子对稀土的协同浸取作用，研发了铝盐与低价无机盐的协同强化浸取新工艺。该工艺显著降低了浸取剂浓度和污染物发生量以及后续富集分离的压力，浸出液中的稀土采用萃取与沉淀相结合的方法富集分离，铝循环利用；我们也提出了氯化钙-硫酸铝分阶段浸取新工艺，其氯化钙浸出液可以直接用石灰沉淀稀土，消除了硫酸根对产品纯度的影响，减少了萃取分离的比例。新工艺获得的产品纯度高，氧化铝含量低于0.03%，稀土浸取率和铝循环利用率均大于95%。浸取稀土后尾矿中的吸附态铝在后续水浸洗过程中十分稳定，但随着石灰水浸pH升高逐渐向胶体和颗粒聚集态氢氧化物转变而稳定在矿层中，流出水质达到环保要求，无水土流失风险。