The coloring of geopolymers by the addition of copper compounds

The development of a new coloring technique is desirable to increase the commercial value of geopolymers. Selected copper compounds, i.e. Cu(OH)2, CuO, Cu2O, CuCO3∙Cu(OH)2∙H2O, CuCl2∙2H2O and CuSO4∙5H2O, were added to the initial reactants in order to color the geopolymers in the same manner as naturally occurring minerals. When Cu(OH)2, CuO and Cu2O were used, these compounds remained in the geopolymer matrix following hardening of the material. On the contrary, CuCO3∙Cu(OH)2∙H2O, CuCl2∙2H2O and CuSO4∙5H2O were not detected in the final products. XAFS analyses were performed to investigate the local structure of copper in the geopolymers produced. The results showed that the copper spectra of geopolymers incorporating Cu(OH)2, CuO and Cu2O correspond to those of pure Cu(OH)2, CuO and Cu2O, respectively. However, when CuCO3∙Cu(OH)2∙H2O, CuCl2∙2H2O and CuSO4∙5H2O were added, the copper generated spectra similar to that of the mineral chrysocolla ((Cu, Al)2H2Si2O5(OH)4∙nH2O) than the respective copper compounds.