Arsenic trisulfide (As₂S₃), in both amorphous and crystalline form, is a significant arsenic-containing compound naturally occurring in mine waste rock or generated as metallurgical waste. It is typically unstable in the enviroment, especially under alkaline and oxidizing conditions, which is a significant barrier to fixation of arsenic present in metallurgical waste streams in the form of arsenic trisulfide. Our previous study has shown the effect of different factors on the kinetics and mechanisms of arsenic and sulfur release from amorphous As₂S₃. To assess the effect of crystallinity on the stability of arsenic trisulfide, a series of laboratory leaching tests were performed with crystalline orpiment under fully controlled conditions. The experimental results showed that the release of arsenic and sulfur increased with pH, dissolved oxygen concentration, and temperature, but the release rates were much slower than those of amorphous arsenic trisulfude. The speciation analyses indicated that arsenic was present in the leachates as arsenite, which was subsequently oxidized to arsenate to different extents; thiosulfate was the main soluble sulfur species, which was converted to sulfate via oxidation and disproportionation pathways. The kinetic modeling suggested that the arsenic release process is a mixed-control reaction, in which the surface chemical reaction and the diffusion of dissolved oxygen through a product layer control the arsenic release rate. The solid surface characterization supported the presence of an arsenic-deficient phase enriched in elemental sulfur on the solid surfaces. The product layer acted as a barrier to the diffusion of reagents, as evidenced by the leaching being sensitive to the removal of elemental sulfur.

三硫化二砷 (As ₂ S ₃ )，以无定形和结晶形式存在，是一种重要的含砷化合物，天然存在于矿山废石中或作为冶金废料产生。它通常在环境中不稳定，尤其是在碱性和氧化条件下，这对于以三硫化二砷形式存在于冶金废物流中的砷的固定是一个重要的障碍。我们之前的研究表明，不同因素对从无定形 As ₂ S _{3 中}释放砷和硫的动力学和机制的影响. 为了评估结晶度对三硫化二砷稳定性的影响，在完全控制的条件下对结晶雌性进行了一系列实验室浸出试验。实验结果表明，砷和硫的释放量随pH值、溶解氧浓度和温度的增加而增加，但释放速度远慢于无定形三硫化二砷。形态分析表明，浸出液中的砷以亚砷酸盐的形式存在，随后被不同程度地氧化为砷酸盐；硫代硫酸盐是主要的可溶性硫物质，通过氧化和歧化途径转化为硫酸盐。动力学模型表明砷释放过程是一个混合控制反应，其中表面化学反应和溶解氧通过产物层的扩散控制砷的释放速率。固体表面表征支持在固体表面上存在富含元素硫的缺砷相。产物层充当试剂扩散的屏障，正如浸出对元素硫的去除敏感所证明的。