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在直接氰化过程中,含银的硫化矿石常常显示出难选特性。即使经过长时间磨矿和长时间的氰化,贵金属的回收率仍然很低,这主要是由于银是以一种可溶性较差的硫代硫酸银盐的形式存在的。因此,为了获得满意的回收率,经常采用焙烧和熔炼法来处理这些矿石,这样又产生了严重的环境污染;或将矿石在氰化前进行湿法氧化或生物氧化。这些方法的主要缺点是在后续的氰化作业前,要添加大量和石灰来中和矿浆以保证适宜的pH值。在Clausthal工业大学选矿研究所的研究表明,采用高压釜湿法氧化和用一段工艺回收贵金属的联合方法非常有效,在联合工艺中湿法氧化是在高温和高的氧分压条件下,在盐水溶液中进行的,所以,一些贵金属将以氯络合物的形式溶解在溶液中。银的溶解度受温度和盐水中盐浓度的影响。制备盐水采用氯化钠和氯化钙,因此,可调节浓度,以便使浓度与所处理矿石中的贵金属含量相匹配。在湿法氧化过程中,硫化物被氧化成元素硫或硫酸盐。砷则以一种难溶的砷酸盐形式沉淀,因而可以安全地排放。
In direct cyanidation, silver-containing sulphidic ores often exhibit refractory properties. The recovery of precious metals remains low, even after prolonged grinding and long periods of cyanidation, mainly due to the silver being present in the form of a poorly soluble silver thiosulfate salt. Therefore, in order to obtain satisfactory recoveries, roasting and smelting processes are often used to treat these ores, which in turn leads to serious environmental pollution; or to wet-oxidize or bio-oxidize ores before cyaniding. The main disadvantage of these methods is that a large amount of lime is added to neutralize the slurry to ensure a suitable pH before the subsequent cyanidation. Research at the Mineral Processing Institute at Clausthal Polytechnic University has shown that a combination of wet oxidation in an autoclave and recovery of precious metals by a process is very effective. Wet oxidation in the combined process is carried out under high temperature and high oxygen partial pressure in the presence of salts Aqueous solution, some of the noble metal will be dissolved in solution in the form of a chloro complex. The solubility of silver is affected by temperature and salt concentration in the brine. Salt water is prepared using sodium chloride and calcium chloride, so the concentration can be adjusted to match the concentration with the precious metal content in the ore being processed. During wet oxidation, the sulfide is oxidized to elemental sulfur or sulfate. Arsenic precipitates in the form of a poorly soluble arsenate and can therefore be safely discharged.