Insights into Sorption–Mineralization Mechanism for Sustainable Granular Composite of MgO-CaO-Al2O3-SiO2-CO2 Based on Nanosized Adsorption Centers and Its Effect on Aqueous Cu(II) Removal

Although copper is needed for living organisms at low concentrations, it is one of the pollutants that should be monitored along with other heavy metals. A novel and sustainable composite mineralizing sorbent based on MgO-CaO-Al2O3-SiO2-CO2 with nanosized adsorption centers was synthesized using natural calcium–magnesium carbonates and clay aluminosilicates for copper sorption. An organometallic modifier was added as a temporary binder and a source of inovalent ions participating in the reactions of defect formation and activated sintering. The sorbent-mineralizer samples of specified composition and properties showed irreversible sorption of Cu2+ ions by the ion exchange reactions Ca2+ ↔ Cu2+ and Mg2+ ↔ Cu2+. The topochemical reactions of the ion exchange 2OH− → CO32−, 2OH− → SO42− and CO32− → SO42− occurred at the surface with formation of the mixed calcium–copper carbonates and sulfates structurally connected with aluminosilicate matrix. The reverse migration of ions to the environment is blocked by the subsequent mineralization of the newly formed interconnected aluminosilicate and carbonate structures.

Sorption of Cu2+ Ions by Bentonite Modified with Al Keggin Cations and Humic Acid in Solutions with pH 4.5

The sorption of Cu2+ onto bentonite modified with Al Keggin cations and humic acid from CuCl2 solutions at pH 4.5 was studied. Modification of Na-bentonite with Al Keggin cations was found to result in an increase in the basal spacing of montmorillonite from 1.29 nm for N-form to 1.85 and 1.78 nm for HAl13 and Al13 forms respectively, in a reduction of CEC (cation exchange capacity) and in the formation of additional sites with a variable charge with pHPZC 4.2. Al13-bentonite is not affected by heat. Under the conditions of the experiments at pH of 4.5 Na-bentonite adsorbs more Cu2+ from CuCl2 solutions then Al13 forms of bentonites. The main mechanism of copper sorption on Na-bentonite is the cation exchange Cu2+–Na+. The reduction of CEC of Na-bentonite after modification with Al Keggin cations leads to a decrease in the Cu2+ sorption. pH-dependent sorption sites on Al13-bentonites have a pHPZC of 4.2 and, therefore, under conditions of the experiment have positive charge which prevents Cu2+ sorption. Na-bentonite adsorbs more humic acid solution (HA) then Al13-bentonite and the proportion of adsorbed HA remains constant over the entire concentration range. Treatment of the Al13-bentonite with HA leads to the formation of the additional sorption sites. The amount of sorbed Cu2+ and the percentage of their extraction from solutions by HAAl13-bentonite is similar to those values for Na-bentonite.