Main factors affecting the adsorption of gold by activated carbon

First, the influence of gold and silver concentration in the leachate

Generally speaking, the concentration of gold and silver in the solution is high, and the amount of gold and silver adsorbed by the activated carbon is increased. When the concentration of gold and silver is constant, the amount of gold and silver adsorbed by activated carbon is greatly affected by the adsorption flow rate. When the flow rate is high, the amount of gold loaded on the activated carbon is reduced. Conversely, lowering the adsorption flow rate is advantageous for increasing the gold content of the gold-loaded carbon and reducing the concentration of the adsorbent tail liquid.

Second, the influence of impurity ions in the leachate

In the gold cyanide heap leaching, in addition to gold and silver dissolved in cyanide into the leachate, copper , cobalt , nickel , mercury and arsenic are also dissolved by cyanide to varying degrees. Studies by Fleming and Nicol have shown that the free cyanide concentration in the leachate plays an important role in the adsorption of copper by activated carbon. When the ratio of free cyanide to copper is small, the copper in the leachate is present as [Cu(CN) ₂ ] ^- complex anion, which can be well adsorbed by the activated carbon, resulting in a decrease in the capacity of the activated carbon to adsorb gold. When the ratio of free cyanide to copper in the leachate is high, copper is present in the leachate with [Cu(CN)3] ^{2 -} and [Cu(CN) ₄ ] ^{3 -} series, and activated carbon does not adsorb such high-valent anions. Therefore, the amount of gold adsorbed is less affected. The effect of silver in the leachate on the adsorption of gold by activated carbon is related to the ratio of silver to gold. When the silver/gold ratio is equal to 1, the gold adsorption capacity of activated carbon is slightly reduced. When the silver/gold ratio is greater than 2, the capacity of activated carbon to adsorb gold is significantly reduced. In short, a small amount of copper, cobalt, nickel, zinc, etc. in the leachate does not seriously affect the adsorption of gold on activated carbon, but due to the adsorption of these impurity ions, occupying the position of the active group, the amount of gold and silver adsorbed by activated carbon is reduced. .

Third, the effect of pH of the leachate on the adsorption of gold

When the pH of the leachate is between 2.5 and 5.0, the loading of activated carbon is the largest. When the pH is greater than 6, the loading of activated carbon decreases with the pH of the leachate, but it is not obvious. Since pH <9.0, cyanide (CN ^- ) is easily hydrolyzed into highly toxic hydrogen cyanide (HCN) gas, which is harmful to the health of operators and increases the consumption of cyanide. Therefore, in cyanide heap leaching, pH is generally controlled. In the range of 9.5 to 10.5, the effect of pH on the amount of gold supported on the activated carbon is not too obvious in this pH range.

In addition to the above-mentioned influencing factors, the type of activated carbon differs in its ability to adsorb gold. It is generally believed that coconut shell carbon has stronger adsorption power than apricot kernel carbon, and fine particle carbon has higher gold content than coarse particle carbon. In actual operation, the amount of gold contained in the carbon is only one of the factors that should be considered. The mechanical strength and pressure drop of the carbon should also be considered comprehensively.

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