Phase Reconstruction And Non-cyanide Leaching Of High Arsenic And High Sulfur Gold Calcine In Alkali Mediums

As a typical refractory gold ore,high arsenic and high sulfur gold ore has gradually become one of the primary resources for gold industry in China.The research on high efficiency and clean treatment of high arsenic and high sulfur refractory gold ores is of great significance for its large-scale development and utilization,and to alleviate the increasing shortage of easily treated gold resources.The two-stage roasting-cyanide leaching process is one of the commomly used processes for high arsenic and high sulfur gold ores.However,due to the presence of gold inclusions in the second-stage calcine,the cyanide leaching ratio is low and the gold in the tailings is difficult to recover.Moreover,the acute toxicity of cyanide can result in environmental pollution and human health hazard.In this study,the two-stage calcine was studied for a high arsenic and high sulfur gold ores from Hunan Province.The alkalizing roasting-alkaline hydrothermal pretreatment process was proposed by studying the physical properties of calcine and its gold-encapsulation mechanism in detail.After the reconstitution of the calcine,the gold inclusions in the calcine can be efficiently dissociated,and the reconstituted slag was leached by thiosulfate instead of the highly toxic cyanide.Therefore,a new method of high-efficiency and clean gold extraction for a high arsenic and high sulfur gold ore was proposed.And the study has made the following progress:（1）Chemical composition analysis,phase composition analysis,morphology analysis,particle size distribution analysis and other measurements were used to identify the physical and chemical properties of the calcine,the occurrence forms of gold,and the gold-encapsulation mechanism.It was found that gold was mainly encapsulated in densely structured hematite in fine particles,and some hematite was encapsulated in quartz.Therefore,the presence of these inclusions led to a low ratio of calcination cyanide leaching of gold.（2）The conversion behavior of hematite in alkalization roasting and alkaline hydrothermal reaction was ascertained.The conversion process was Fe₂O₃→Na_0.9(Fe_0.9Si_0.1)O₂→Fe₂O₃·xH₂O.Based on this,a new process of Na₂CO₃alkalization roasting-NaOH alkaline hydrothermal treatment for calcine was proposed.The hematite and silicon-containing phases in the calcine were converted into Na_0.9(Fe_0.9Si_0.1)O₂ and Na₂SiO₃ by alkalization roasting,respectively.Further,Na_0.9(Fe_0.9Si_0.1)O₂ can be further converted into loose porous amorphous Fe₂O₃·xH₂O and water-soluble Na₂SiO₃ by alkaline hydrothermal treatment.Thereby,the gold inclusions in the hematite and silicon-containing phases were sufficiently dissociated,and the separation of silicon and sodium from the slag phase was achieved.Using the conventional cyanidation to leaching the pretreated sample,the leaching ratio of the gold increased from the initial 78.30%to 99.36%,and the gold content in the tailings decreased to 0.60 g/t.It showed that the gold leaching effect was remarkable.Then the pretreated sample was leached by thiosulfate instead of highly toxic cyanide,and the optimal thiosulfate leaching gold conditions were determined by single factor experiments.The leaching ratio of gold was 82.31%,and the gold content in the tailings was 7.99 g/t.（3）The paper systematically carried out the optimization research on the Na₂CO₃alkalization roasting-NaOH hydrothermal treatment process for the calcine,and determined the optimal reaction conditions.The Fe₂O₃ and SiO₂ in the calcine were nearly completely converted to Na_0.9(Fe_0.9Si_0.1)O₂ and Na₂SiO₃ under the optimal alkalization roasting conditions.And under the optimal hydrothermal treatment conditions,the removal ratio of sodium and silicon in the alkalized roasting slag were95.13%and 84.40%,respectively.After the phase reconstitution,iron mainly exist in the form of amorphous Fe₂O₃·xH₂O.The slag after the hydrothermal treatment was leached by thiosulfate,and the gold leaching ratio was 89.19%.However,the total leaching ratio of gold can reach 96.98%after three times of thiosulfate leaching.