Recovery of Gold from Arsenic Pyrite Concentrate by Cyanide-Carbon Adsorption Method (II)

Cyanidation pre-leaching test:

Pre stirred cyanidation leaching experimentally obtained data about your arsenopyrite ores of ferrous metals. Put 200 grams The concentrate is placed in 600 ml of solution and leached for 24 hours. The solution contains sodium cyanide. 10 pounds / Ton lime as protective base, pH 11.

The method of atomic absorption analysis using expensive gold and silver in the solution, with conventional fire assay analysis leached residue. The analysis indicated that the gold and silver recovery rates obtained from the test were 95% and 81%, respectively .

In order to determine the effect of leaching time on the recovery of gold and silver, a cyanide leaching test similar to the above was performed. In an open container 400 grams Concentrate and lime 20 pounds / ton of ore) and containing NaCN ( 10 pounds / ton of solution) 1200 ml of water was mixed and stirred for 96 hours. After 24 hours of leaching , the recovery of gold and silver was determined by decanting the noble solution and Chddy analysis. Instead of the discharged solution, an equal amount of fresh leaching agent having the same cyanide concentration can be used and stirring is restarted. The content of precious metals in the final leaching residue was analyzed by a gold test method. The data in Table 2 shows that the higher recovery of gold and silver in the arsenopyrite concentrate can be obtained by stirring cyanide for 72 to 96 hours.

Table 2   Effect of leaching time on recovery of precious metals from cyanidation

Cumulative leaching time (hours)

Cumulative results of leaching (% of total)

gold

silver

twenty four

85.00

78.60

48

94.70

84.70

72

96.40

88.50

96

96.90

90.70

 

In order to determine the distribution of the remaining precious metals, 0.7 ounces / ton and silver 0.6 ounces / ton of leaching residue was sieved and the results are shown in Table 3 .

In the level distribution of the gold particles indicate the remaining tailings sulphide minerals closely associated with the gold, and then finely ground to improve the recovery of gold is not as -35 mesh and -325 mesh mineral leaching results are - like of. The -325 mesh has a higher silver content in the grain size, indicating that the silver component of the silver-containing mineral is not suitable for cyanidation. Top flow percolation leaching;

In order to determine whether the concentrate is suitable for cyanide leaching, a top-flow percolation leaching test was performed. 2000 grams Concentrate and 20 grams Lime placed in a diameter of 2.5 inches The glass columns are mixed to form an approximately 14 inches Deep bed. With NaCN per ton 6.0 pounds The solution is leached out of the concentrate and the leachate is pumped from the upper end through the bed at a flow rate of 1.2 liters / hour. Use a fixed tank to hold the precious liquid that passes through the leaching column, and then pass the precious liquid through the five columns in series, each column is loaded 14.6 grams -6 mesh ~ +16 mesh coconut shell activated carbon. The lean liquid is recycled to the leaching column. By atomic absorption analysis method every 6 hours - and silver content of the pregnant solution views lean liquid sample. At the beginning, the precious liquid obtained by leaching for 40 hours contained an average gold content of 9.5 ppm and a leaching rate of 32% . In contrast, the gold leaching rate obtained from the stirred cyanidation leaching test with the same leaching time was 90% . According to the following reaction formula, the dissolution rate of gold in the percolation leaching test is slower because there is not enough oxygen to dissolve the gold.

4Au+8CN - +O 2 +2H 2 O → 4Au ( CN ) 2 - +4OH -            ( 1 )

2Au+4CN - +O 2 +2H 2 O → 2Au ( CN ) 2 - +H 2 O 2 +2OH -     ( 2 )

To verify this determination, a small amount of H 2 O 2 was added to the leachate to provide oxygen for the dissolution reaction. Adding 30% H 2 0 per day of depleted liquid - ml per liter can significantly increase the dissolution rate of gold, and sodium cyanide is not greatly damaged. After leaching for 20 hours, the precious liquid contained an average of 316 ppm of gold , indicating that the gold leaching rate increased by 60% . The gold recovery obtained by a total of 96 hours of diafiltration leaching test was compared with the recovery obtained by stirred cyanidation. These results indicate that in order to achieve a satisfactory recovery rate by diafiltration cyanidation within a certain period of time, air or oxygen must be blown into the concentrate bed during the leaching process.

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