Recycling Galvanic Sludge to Produce Geopolymer Modified with Algae

A new group of geopolymers based on galvanic sewage sludge was synthesized using algae. The sorption properties of the obtained geopolymer materials toward Cu(II), Mn(II), Pb(II), and Zn(II) ions in aqueous solutions were investigated. Algae have good adsorption properties with respect to heavy metals and bind to them irreversibly. Their addition to the geopolymer mass results in a geopolymer in which the C-(N)-A-S-H gel is dominant in the structure, as shown by SEM analysis. Analysis of the FTIR spectra of the geopolymer obtained with the addition of algae before and after sorption of the studied metal ions showed the presence of bands characteristic of geopolymers, proving at the same time that the introduction of algae increases the negative charge on the surface of the geopolymer and the chemisorption of heavy metal ions. The resulting geopolymer material shows excellent removal efficiency for all ions tested, respectively, Cu(II)—96.9, Mn(II)—98.9, Pb—99.7, and Zn(II)—99.5. The sorption process under experimental conditions follows the Langmuir isotherm model. The kinetics of the process are described by a pseudo-second-order kinetic equation, which confirms the contribution of functional groups to the binding of the ions of the studied metals.