焙烧脱硫-火试金法测定铅精矿和铜精矿中金和银

将铅精矿或铜精矿样品30.00g平铺于预先铺有20g二氧化硅的方舟中,于试金炉中在750℃焙烧脱硫60min。将脱硫后的样品混合物转移至黏土坩埚中,加入50g碳酸钠,200g氧化铅,20g四硼酸钠作为助熔剂,4.0g淀粉作为还原剂,搅匀后在表面覆盖约5mm厚的氯化钠,在试金炉中于1 100℃进行熔融(一次试金),获得30~40g的铅扣。将铅扣在850℃进行灰吹,得到金银合粒。将一次试金的熔渣和灰皿粉碎后置于一次试金用的坩埚中,加入40g碳酸钠,20g四硼酸钠,25g二氧化硅及4.0g淀粉,搅匀并在表面覆盖约5mm厚的氯化钠后,再进行火试金和灰吹处理,得到第二颗金银合粒。两次所得金银合粒合并后,用热硝酸(1+7)溶液进行分金。用重量法或原子吸收光谱法测得金量,用差量法得到银量(用电感耦合等离子体原子发射光谱法测定铜、铅、铋、砷和锑等杂质的含量)。回收试验得到金的回收率为99.2%~100%,银的回收率为100%,测定值的相对标准偏差(n=7)为0.37%~2.8%(金)和0.28%~2.4%(银)。

Determination of Gold and Silver in Lead Ore Concentrate or Copper Ore Concentrate by Fire Assay with Desulfurization by Roasting

Sample of lead ore concentrate or copper ore concentrate(30.00 g)was smooth out on a layer of silicon dioxide(20 g)which was priliminarily placed on the bottom of a combustion boat and roasted for 60 min at750℃ in an assay furnace for desulfurization.The desulfurized sample mixture was then transferred to a clay crucible,and a flux mixture containing 50 g Na2 CO3,200 g PbO and 20 g Na2 B4 O7 together with 4.0 g of starch as reductant was added.After thorough mixing,and covering a layer of NaCl with its thickness ca.5 mm,the mixture was fused at 1 100℃in an assay furnace for the 1 st fire assay,and a lead button of 30 to 40 g was obtained.The lead button was cupelled at 850℃and a metal bead of gold and silver was obtained.The molten slag and cupel left from the 1 st fire assay were crushed and placed into the crucible used in the 1 st fire assay,and the 2 nd fire assay and cupellation were carried out in the same way as the 1 st assay and cupellation,except using less amounts of flux mixture(40 g Na2 CO3,20 g Na2 B4 O7 and 25 g SiO2),and a second metal bead of gold and silver was obtained.The two metal beads of gold and silver were put together and treated with hot HNO3(1+7)solution to separate gold from silver and other impurities.The gold was determined by gravimetry or by AAS,and the silver was determined by difference method(the impurities,i.e.Cu,Pb,Bi,As,Sb were determined by ICP-AES).Values of recovery found by test for recovery were in the range of 99.2% to 100% for gold and were 100% for silver,and values of RSDs(n=7)of determination values were ranged from 0.37%to 2.8%for gold and from 0.28%to 2.4%for silver.