Mechanism of action of anti-fouling agent in heap leaching

The mechanism of action of anti-fouling agents is not yet fully understood, and the arguments are not completely consistent. Most of the antifouling agents are considered to function as a crystal nucleating dispersant, a crystal form change agent, and a medium stabilizer.

First, the role of crystal nucleating agent

After the calcium carbonate nucleus adsorbs the anti-fouling agent molecule on the surface thereof, the nucleus in the solution is repulsion due to electron or spatial structure, so that the crystal nucleus in the solution cannot aggregate with each other to form a precipitate, and is in a good dispersed state. For example, adding sodium hydroxide to a solution containing a large amount of calcium bicarbonate having a pH of 7 to 8 immediately produces a large amount of white calcium carbonate crystal precipitate; however, if 2 × 10 ^-5 is added to the solution containing calcium bicarbonate in advance, sodium tripolyphosphate, ratio of sodium hydroxide was added, the solution does not appear in a white precipitate of calcium carbonate crystals, some deterioration of transparency of the solution at this time. It is impossible to dissolve the calcium carbonate precipitate by sodium tripolyphosphate, but to disperse the calcium carbonate nucleus which is invisible to the naked eye in the solution so that it cannot aggregate to form large crystals.

Second, the crystal form change agent

The crystal form of calcium carbonate crystal is originally symmetrical, but when the calcium carbonate nucleus adsorbs the anti-fouling agent molecule on its surface, the crystal form of the calcium carbonate crystal becomes asymmetrical, and grows in the direction of the surface, becoming spherical (see FIG. 1) The addition of such an anti-fouling agent results in a change in crystal form. Asymmetric crystallization reduces the tendency of adsorption on the surface, thereby inhibiting the formation of scale.

Figure 1 Comparison of two calcium carbonate crystals before and after adding anti-fouling agent

(a) No anti-fouling agent calcium carbonate crystals (b) Calcium carbonate crystals after adding anti-scaling agent

Third, the role of medium stabilizer

The presence of unstable elements in the medium promotes the formation of scale. The causes of instability of the medium are various, such as sudden changes in pressure, flow rate, flow pattern, etc., or due to large changes in the concentration of certain components in the medium. When Ca ^{2 +} in the medium or CO ₃ ^{2 -} concentration increases beyond its solubility product is generated CaCO ₃ crystals, but if the added molecules can antifoulant and Ca ^{+ 2} or CO ₃ ^{2 -} Interaction to form a very high stability, solubility, complex or complex salt of a class of substances like, which is bound to make the Ca ^{2 +} or CO ₃ ^{2 -} concentration in the solution stable, artificially created as a result The new solubility of calcium carbonate inhibits or retards fouling because the addition of anti-fouling agents alters the sensitive precipitation-dissolution equilibrium.

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