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Sequential elution. This method was developed by the U.S. Bureau of Min
es and elution is done sequentially with gold being eluted with NaClO which, being a strong oxidant, destroys the gold cyanide complex and liberates the gold. During the tests, strong base resins Amberlite IRA 400, Amberlite IRA 900, Dowex 21K, Dowex MSA-1, and Dowex SBR, were loaded with gold silver and mercury, then eluted sequentially with various eluants. Generally, all five strong base resins behaved similarly. With the first 3 hours, 100% of the mercury was eluted with 2N H2SO4. About 20% of the silver was eluted with the mercury in the case of the Dowex SBR resin; however, no gold was eluted. A subsequent elution with 200 g/l NaCl in 1N HCl removed all the remaining silver from the five resins in 6 hours with less than 10% of the gold being eluted. A final elution with 0.75% NaClO in 150 g/l NaCl plus 5% NaOH removed 93 to 98% of the gold in 9 hours. Figure 6 shows a flowsheet. |
