Research On Cyanide-free Leaching Technology Of Yuanyang Limonite-type Gold And Silver Ore

The limonitic gold-silver ore is a new type of epigenetic gold deposit that has been proved in the past forty years.It belongs to precious metals associated with iron resources which iron average grade is about 35%⁵0%.and the inner associated gold and silver grade is low.Most of them are adsorbed or encapsulated in limonite,which makes it difficult to recovery.Many iron ore dressing plants in China are difficult to realize the comprehensive recovery of associated precious metals in limonitic gold-silver ore due to technical and economic factors,resulting in waste of resources.This paper takes Yuanyang limonitic gold-silver ore as the research object,which provides technical reference for comprehensivly recycling and utilization of gold,silver and iron resources in the limonitic gold-silver ore in China.Mineralogical studies on the limonitic gold-silver ore indicate that the ore has a higher oxidation rate,and the oxides mainly account for 86.6%of the ore.The main minerals are limonite,goethite,h ematite,muscovite,dolomite,calcite and quartz.Gold,silver and iron in the raw ore is the major recycled element.The iron grade is 49.75%,the gold grade is 1.7 g/t,and the silver grade is 103 g/t.Gold is mainly present in the form of isomorphism or adsorption in limonite and gangue minerals,the rest in the form of natural elements and independent minerals;silver is mainly in the form of fluorite ore;iron is mainly in the form of independent minerals such as limonite and hematite.Because the single or combined physical beneficiation method hard to solve the problem that iron concentrate contain 30%of gold and silver.Therefore,wet leaching combined with magnetic separation is used to recover gold,silver and iron in the raw ore.There are four n on-cyanide leaching systems were compared,which was thiourea method,chlorination method,new environmental immersion gold agent and sodium thiosulfate.According to the leaching results of gold and silver in the ore,the copper-ammonia-sodium thiosulfate leaching was selected.The conditions of“copper-ammonia-sodium thiosulfate”leaching system were optimized,and the best leaching conditions were as follows:grinding fineness of-200 mesh accounted for 90.16%,pulp concentration of55%,and the dosage of copper sulfate is 20 kg/t.The dosage of ammonium sulfate is 40kg/t,the initial pH is adjusted to 10 by ammonia solution,the dosage of sodium thiosulfate is 100kg/t,the leaching time is 6h,and the stirring speed is 400r/min.Under the optimal leachi ng conditions,the leaching rate of gold is 87.05%,and the leaching rate of silver is 72.65%in the first leaching phase.Based on large of literature review and verification of experiments,it was found that the Cu₂S produced by the leaching process is the reason why the silver leaching rate cannot be improved,but the oxidation of ferric chloride can dissolve the Cu ₂S on the surface of the leaching slag,then the silver leaching rate have improved.The test results of the ferric chloride dosage condition indicate that the optimal dosage of ferric chloride is 30g/t,the total leaching rate of silver in the ore can be increased to 91.16%in the second leaching phase.Based on the above research,a noval idea of“sodium thiosulfate leaching-ferric chloride surface treatment-sodium thiosulfate leaching-high gradient strong magnetic separation”was proposed,which can comprehensively recovery gold,silver and iron from limonitic gold-silver ore.Under fine grinding conditions,the extraction of gold and silver in the ore by“copper-ammonia-sodium thiosulfate”is used to reduce the gold and silver entrainment in the iron concentrate at the first phase.the second stage leaching,the leaching slag need to be surface treated by ferric chloride to dissolve Cu₂S to improve silver leaching ratio.High-gradient magnetic separation is used to recovery the weak magnetic minerals in the second-stage leaching slag.Finnally the results showed that the total leaching rate of gold is 87.65%,the total leaching rate of silver is 91.63%,the grade of iron is 60.63%,and the total recovery of iron is 73.6%.which realized comprehensive recycling of limonite type gold-silver mine.