钨酸钠溶液直接水热分解制备焦绿石型氧化钨粉体的基础研究

The tungsten-bearing resource in our country is in the most superior position in the tungsten mineral resources in the world. The separate amount of tungsten production and its consumption in China both rank the first in the world. However, The industrial prevailing extractive technology for tungsten oxide in China has still many problems such as long flowsheet, high energy consumption, high base or acid consumption and relatively serious environmental pollution,although many progresses have been achieved during the past over half century. On the other hand, pyrochlore-type tungsten trioxide powder has great potential in the application of advanced functional materials in the near future. Under these considerations, this proposal mainly investigates: 1)the physiochemical properties of sodium tungstate solution and their corresponding controlling methods, 2)the fundamental of the crystallization of tungsten trioxide hydrates from the sodium tungstate solution, 3)controlling methods for the hydrothermal precipitates; and 4) the technological prototype of the direct hydrothermal precipitation of tungsten trioxide from alkaline sodium tungstate solution. The accomplishment of this basic research may realize the direct hydrothermal precipitation of tungsten trioxide powder from the industrial sodium tungstate solution, and thus allow the recycling use of the alkali. This noval technology will eliminate completely the formation of a large amount of salts,ammonium and nitrogen-bearing waste water and gases, as it may cancel the intermedium preparation processes of ammonium tungstate and ammonium paratungstate acquired in the present industrial extrative process of tungsten oxides.So this investigation will pave the way for a new generation technology of the green tungsten extractive metallurgy with short flowsheet,high efficiency and low consumption.

钨资源是我国在国际上最具优势地位的矿产资源之一，我国钨的产销量均已居世界首位。但目前我国氧化钨的提取冶金流程长、能耗高、碱（酸）消耗量大、外排盐和氨氮废水,治理难、环境污染重；同时焦绿石型氧化钨粉体在众多先进功能材料方面的应用潜力巨大，但国内外尚无直接从碱性的钨酸钠溶液制备氧化钨粉体的研究报道。因此，本项目拟重点研究：1）钨酸钠溶液的物理化学性质及其调控方法；2）钨酸钠溶液水热析出氧化钨粉体的结晶学基础；3）水热产物性质的调控方法；4）建立钨酸钠溶液直接水热析出氧化钨粉体的技术原型。本项目的研究成果将有望实现工业钨酸钠溶液直接水热析出焦绿石型氧化钨粉体，从而实现氧化钨提取冶金体系中碱的闭路循环，取消现行工业生产中中间产物-钨酸铵和仲钨酸铵的制备过程，从源头上彻底消除大量无用盐以及含氨氮废水和废气的产生，为开发新一代短流程、高效、低耗和清洁的钨提取冶金技术奠定理论基础。

项目重点开展了弱碱性钨酸钠溶液中含钨离子种类及其调控方法、钨酸钠溶液直接水热结晶析出焦绿石型氧化钨的结晶机制及其产物物化性质的调控等三方面的研究。获得了如下主要研究结果：1）明晰了弱碱性钨酸钠溶液体系中含钨阴离子的种类及其总体转化规律，当钨酸钠溶液的碱性逐渐变弱时，溶液中的主体含钨阴离子将由WO42-逐渐依次转化为W2O72-、W7O246-以及H2W12O4210-等离子；2）确定了从弱碱性钨酸盐水溶液体系直接水热结晶析出焦绿石型氧化钨的有利生长基元为W7O246-，并确定了WO42-向W2O72-的转化是钨酸钠溶液中其他含钨阴离子向W7O246-离子转化的控制步骤，而添加能使溶液稳定保持在弱碱性体系的酸化剂能强化其他含钨阴离子向W7O246-离子的转化；3）钨酸钠溶液体系pH值及其稳定范围、酸化剂种类、晶种以及结晶助剂等直接影响焦绿石型氧化钨结晶过程的成核、长大和附聚过程，进而影响结晶产物的粒度和形貌；4）在相同水热条件下，添加有机酸能显著强化WO42-离子向W2O72-的转化，大幅增加溶液中W7O246-离子浓度，有利于提高钨结晶率和获得粒度分布均匀、形貌规整的超细焦绿石型氧化钨粉体；5）基于焦绿石型氧化钨水热结晶机制的研究，通过添加酸化剂调控钨酸钠溶液中含钨离子种类及其浓度，并结合适当的结晶助剂，实现焦绿石型氧化钨结晶过程中成核、长大和附聚等子过程的匹配，形成了从弱碱性钨酸盐溶液中直接水热结晶析出焦绿石型氧化钨的技术原型。在优化实验条件下，可获得杂质含量低、粒度分布均匀、平均粒径0.5μm以下的焦绿石型氧化钨粉体，溶液中钨结晶率高达98%，结晶母液可返回钨精矿的浸出过程循环使用，从而有望高效清洁实现钨的提取冶金过程，达到环境效益和经济效益的有机统一；6）由钨酸钠溶液水热结晶产物通过浸渍-提拉法制备的焦绿石型氧化钨薄膜具有良好的电致变色性能，300°C煅烧1h后的薄膜在885nm处的着色效率高达68.5cm2c-1。项目研究结果对钨酸盐溶液结构调控和高效清洁提取APT具有重要意义。