金精矿微波焙烧-自浸出过程中单质硫的生成与作用机制

In view of the serious environmental pollution situation in traditional cyanide gold leaching process, gold concentrate will be treated by microwave roasting to generate elemental sulfur. In this process, elemental sulfur will react with lime to form leaching reagent, which can be used in non-cyanide self-leaching of gold. The thermodynamic studies on microwave roasting of gold bearing sulfide minerals such as pyrite and arsenopyrite will be performed at different roasting atmosphere. The existing forms of arsenic and sulfur in the roasting products will be assayed, and the thermodynamic conditions of elemental sulfur formation will be investigated. The phase transformation of elemental arsenic and sulfur will be studied to illustrate the mechanism of formation of elemental sulfur. In addition, kinetic studies on microwave roasting of gold concentrate will be conducted to establish the reaction control model. The effect of valence state changes of elemental sulfur and properties of roasted product on leaching performance will be investigated. The relationship among roasting conditions, properties of roasting products and leaching rate of gold will be studied. The reinforcement mechanism of microwave roasting will be investigated to optimize self-leaching performance. The study on the mechanism of microwave roasting and non-cyanide self-leaching meets the requirement of developing efficient green-mines, and is expected to obtain creative achievements in the area of high-efficient and clean gold leaching. Therefore, the proposed study has important significance in sustainable development of gold mines in China.

针对传统氰化浸金工艺环境污染严重的现状，本研究拟对金精矿进行微波焙烧，使其中硫化矿物中的硫以单质形式产出，并将单质硫与石灰反应形成浸金试剂，实现金的非氰自浸出。通过对金精矿中典型载金硫化矿物黄铁矿、砷黄铁矿等在不同气氛下的焙烧热力学研究，分析硫、砷等元素的焙烧产物形式，揭示单质硫生成的热力学条件；研究金精矿微波焙烧的物相转变及硫、砷等元素赋存状态变化规律，阐明单质硫的生成机理；对金精矿的微波焙烧动力学研究，建立焙烧反应控制模型；研究自浸出过程中单质硫的价态变化和焙砂性质对浸出过程的影响规律，优化自浸出过程，探究微波焙烧条件-焙砂性质-金自浸出率三者的关系，揭示微波焙烧对自浸出过程的强化机制。金精矿的微波焙烧和非氰自浸出的研究顺应我国高效、绿色矿山开发的需求，有望在黄金的高效、清洁提取方面取得原创性成果，对我国黄金矿山的可持续发展有着重要的意义。

氰化法是从矿石中提取黄金的主要方法，但氰化物的毒性给黄金生产企业带来了巨大的安全和环保压力。本研究提出利用金精矿微波热分解生成的单质硫来实现金的非氰自浸出这一新技术，探讨了金精矿中的载金硫化物微波热分解过程中单质硫的释放规律和生成机理；阐明了单质硫在碱性条件下的浸金机理及微波焙烧对金浸出过程的强化机制，完善了金精矿微波中性焙烧-自浸出的基础理论体系。研究表明金精矿热分解生成的硫单质主要来源于黄铁矿，其在惰性气氛中的相变温度为500℃，高砷金精矿热分解过程中存在脱砷和脱硫两个吸热反应，单质硫的生成量较少。黄铁矿具有优良的微波吸收能力，随着焙烧温度升高立方晶系的黄铁矿逐渐转变为六方晶系的磁黄铁矿，部分硫元素以气态硫单质形式产出，相变过程主要发生在500-750℃；当温度升至900℃时，硫的转化率为48%，S/Fe摩尔比降至1.09。微波加热使磁黄铁矿相出现的温度降低了约100℃，促进了黄铁矿中硫元素赋存状态的转变，降低了热分解反应活化能。微波中性焙烧使载金硫化物中原本致密的矿物颗粒变得疏松多孔，颗粒内部出现大量空洞和孔隙，在温度为700℃下焙烧30min后，孔隙率由32.9%升至48.9%，使得被硫化物包裹的金颗粒充分暴露，增加了金与浸出剂的接触面积。在惰性气氛中，微波加热处理使黄铜矿转变为六方硫铁铜矿、硫化亚铁和硫化铜矿物，强化了其在碱性硫代硫酸盐体系中铜的溶出。探讨了载金硫化物微波中性焙烧-自浸出的可行性，利用生成的单质硫制备碱性含硫试剂进行浸出试验，在铜氨络合物的作用下金的浸出率可达91.98%。研究发现碱性含硫试剂在金表面发生明显吸附，浓度越高吸附量越大，金表面钝化越严重；制备碱性含硫试剂所用硫源对金的溶出速率影响不大，升高温度或添加铜氨络离子可促进金表面含硫钝化层的溶解，显著提高金的溶出速率，金溶出后以硫金络合物的形式存在。本研究为非氰浸金提供了新的思路，顺应我国高效、绿色矿山开发的需求，对我国黄金矿山的可持续发展有着重要的意义。