The Removal of Cu(II) by Composite Zeolite-humate Sorbent in the Presence of Extraneous Electrolytes

Abstract

In thermal power engineering, the issue of removal of heavy metal ions from circulating water, which was formed as a result of corrosion of equipment made of non-ferrous metals, is very acute. The presence of other electrolytes, especially the hardness salts, significantly affects the degree of heavy metal ions removal in processes where the main mechanism is ion exchange. With a significant excess of calcium salts, it is practically impossible to achieve a noticeable reduction of copper ions content using cation exchange resins. One of the alternative methods for solving this problem is the synthesis of a composite sorbent on the basis of existing porous natural carriers, by treating it with a modifier in order to obtain a surface that has a high affinity for the pollutants. Zeolite is a natural alumosilicate mineral that has ion-exchange properties and is widely used as a sorbent for metals. Raw zeolite has relatively low sorption capacity to heavy metal ions though it can be improved via impregnation by hymic acids solution followed by their intraparticle precipitation. Humic acids themselves can bind metal ions in complexes but their application in pure form is not practical as they are in colloid form. Sorption properties of a composite sorbent based on zeolite and humic acids with respect to Cu(II) at sorption from monocomponent model solutions and in the presence of Na⁺, Ca²⁺, Fe³⁺ as extraneous cations were studied. The presence of sodium salts had little effect on the residual copper concentration. In the presence of calcium and iron salts, the sorption of copper was depressed considerably. The composite sorbent had higher specific sorption capacity and made it possible to achieve lower residual copper concentrations compared to unmodified zeolite. The values of the Cu (II) distribution coefficient between the liquid and solid phases in solutions of different salt composition were calculated. It was 1,5…2 times higher for composite sorbent than for non-treated zeolyte. The relationship between the value of the distribution coefficient and the concentration of the extraneous electrolyte in logarithmic coordinates is linear.