含碳微细粒金矿是世界难处理金矿主要类型, 且储量巨大, 矿石中的有机碳、 石墨碳能吸附溶液中的金氰络合物, 因而含碳金矿在浸出之前需进行预处理。 氧化焙烧是应用时间最长、 可靠性和适应性最好的预处理工艺, 已经成功的用于生产实践。 针对传统氧化焙烧法存在生产成本高, 收尘系统复杂等不足, 近年来国内外学者在焙烧工艺和设备方面进行了大量的研究工作, 取得了丰硕的研究成果, 为氧化焙烧技术的发展注入了新的活力。 但关于焙烧理论方面的研究较少, 研究方法也比较单一, 尤其是对于焙烧过程的相关理论研究比较薄弱, 这在一定程度上影响了氧化焙烧技术的发展。 焙烧时间是影响焙烧效果的关键因素, 决定化学反应进度及物相变化程度。 在不同时间条件下(焙烧温度650 ℃), 对含碳微细粒金矿石进行焙烧-浸出试验, 首次采用X射线衍射(XRD)、 扫描电镜(SEM)、 能谱分析(EDS)和孔结构分析等手段对含碳金矿及焙砂进行分析表征, 进而揭示氧化焙烧过程中碳质物的氧化、 矿石晶体结构变化、 物相变化等对金浸出效果的影响机理。 工艺矿物学研究表明: 矿石中主要矿物有石英、 白云石、 方解石、 绢云母、 高岭石、 黄铁矿和石墨等; 矿石中自然金粒度微细, 以5~10 μm粒级为主, 部分微粒自然金被石英、 碳质组成的碎屑包裹; 碳质(有机碳和石墨碳)含量高、 粒度细, 且与脉石矿物紧密共生。 焙烧-浸出试验结果表明: 原矿直接浸出时, 金浸出率仅为12.50%, 碳质的“劫金”作用显著; 随着焙烧时间的增加, 金的浸出率先逐渐增大后变化平稳, 焙烧时间为2 h时, 金浸出率最高; 当焙烧时间为1 h 时, 绢云母发生了脱羟基变化, 高岭石分解生成蒙脱石, 黄铁矿氧化为赤铁矿, 碳质(有机碳和石墨碳)氧化且产生CO₂, 但未完全氧化, 此时焙砂中石英的 d₁₀₀和 d₁₀₁值以及平均孔径较小, 不利于浸出剂的扩散, 导致金浸出率仅为58.09%; 当焙烧时间为1.5 h 时, 白云石开始分解, 碳质已完全燃烧, 产生的CO₂使微孔数量增多, 有利于浸出剂的扩散, 此时金浸出率增加到73.34%; 当焙烧时间为2 h时, 白云石分解较完全, 焙砂中有MgO生成, 此时焙砂中石英的 d₁₀₁值达到最大值(4.255 03 nm), 焙砂松散密度变大且孔容和平均孔径达到最大值, 分别为0.009 954 cm³·g^-1和6.640 80 nm, 焙砂中产生的微孔最多, 增加了浸出剂的扩散通道, 有利于金的浸出, 金浸出率也达到了最大值(91.28%); 当焙烧时间为3 h时, 焙砂表面生成Ca₂SiO₄和CaSO₄等在高温时易形成低熔点物质, 发生微弱的烧结现象, 导致颗粒内部的微孔被填充、 闭合, 微孔减少, 孔容和平均孔径降低, 内部结构变得致密, 不利于浸出剂的扩散, 同时造成金的浸出率下降。

The carbonaceous fine-grained gold ore is one of the main types of refractory gold deposits in the world with huge reserves. The organic carbon and graphite in the ore can adsorb the cyanide complex in the solution, so the carbon-bearing gold ore needs to be pre-treated before leaching. Oxidation roasting is the best pretreatment process with the longest application time, the best reliability and the adaptability. It has been successfully used in the production practice. Traditional oxidation roasting method has the disadvantages of high production cost, complicated dust collecting system and so on. In recent years, domestic and foreign scholars have done a lot of research work on roasting process and equipment, and achieved fruitful research results, which has injected new vitality into the development of oxidation roasting technology. However, there are few researches on the theory of roasting and the research methods are relatively simple. Especially, the relevant theory of roasting process is relatively weak, which affects the development of roasting technology to a certain extent. Roasting time is the key factor that affects roasting, which determines the progress of chemical reaction and the degree of phase change. In this study, under different time conditions (roasting temperature 650 ℃), the carbon-containing fine-grained gold ores were roasted and leached. For the first time, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy spectrum analysis (EDS) and pore structure analysis were used to analyze and characterize the gold. Then the mechanism of the oxidation of carbonaceous material, the change of crystal structure and the change of phase on the gold leaching during the oxidation roasting process were also revealed. Process mineralogy study showed that the main minerals are quartz, dolomite, calcite, sericite, kaolinite, pyrite and graphite; The native gold in the ore is fine with the grain size of 5~10 μm, which is wrapped by quartz and carbonaceous debris. Carbonaceous (organic carbon and graphite carbon) has high content and fine grain size, and is closely associated with gangue minerals. The result of roasting-leaching experiment shows that the leaching rate of gold was only 12.50% when the raw ore was directly leached, and the role of “carbonaceous robbery gold” was significant. With the increase of roasting time, the leaching rate of gold first increased and then changed smoothly. When the roasting time was 2 h, the leaching rate of gold was the highest. When roasting time was 1 h, the reaction of dehydroxylation was occurred on sericite, kaolinite was decomposed into montmorillonite, the pyrite was oxidized to hematite, and carbonaceous (organic carbon and graphitic carbon) was oxidized and produced CO₂ but was not fully oxidized. At this moment, the d100 and d101 values and the average pore size of quartz were small, which was unfavorable to the diffusion of leaching agent, resulting in the gold leaching rate at only 58.09%. When the roasting time was 1.5 h, the dolomite began to decompose; the carbonaceous material has completely burned. CO₂ produced increased the number of micropores, which was conducive to the proliferation of leaching agent, so the gold leaching rate increased to 73.34%. When roasting time was 2 h, dolomite decomposed completely, and MgO was formed. The d₁₀₁ value of quartz reached the maximum (4.255 03 nm), the calcareous bulk density became higher; Furthermore, the pore volume and average pore diameter reached the maximum, which were respectively 0.009 954 cm³·g^-1 and 6.640 80 nm. The most pores produced in calcine increased the diffusion channel of leaching agent, which was beneficial to the gold leaching. The gold leaching rate also reached the maximum (91.28%). When the roasting time was 3 h, the surface of sample produced Ca₂SiO₄, CaSO₄ and so on which were easy to form low melting point material at high temperature, so weak sintering occurred. The micropores inside the particles were filled and closed, the micropores, the pore volume and the average pore size reduced. The internal structure became dense, which was not conducive to the proliferation of leaching agent, causing the decrease of the gold leaching rate.