Effect of partial replacement of volcanic ashes by waste iron powder on the properties of phosphate inorganic polymers

This study focuses on the effect of partial replacement of volcanic ash (VA) by waste iron powder in the synthesis of phosphate inorganic polymers (PIPs) based of volcanic ashes. For this purpose, 0, 5, 10, 15, and 20% of the waste iron powder were substituted for those of two volcanic ash named MaJ and Mbo. Subsequently, all the powders were mixed with a solution of H₃PO₄ (6 M) with a liquid/solid mass ratio of 0.45. The raw materials were characterized by XRF, BET, XRD and FTIR. In addition to these characterization techniques, the obtained synthesis products were also characterized by Optical Microscopy. The properties of the 28-day old specimens were evaluated by determining the compressive strength, density, percentage water absorption and porosity. The results obtained show that the increase in iron powder waste leads to a decrease in compressive strength and density and, in parallel, an increase in porosity and water absorption. In combination with the BET analyses, the observation of the optical micrographs shows that for a partial replacement of 10% of the ash powder (Mbo) by the iron powder waste leads to an increase in the specific surface of the synthesis products and an increased presence of voids within the Mbo-based specimens. On the other hand, for the same content, we observe an occupation of the pores within the MaJ-based specimens. All these results show that iron powders wastes lead to an expansion of the pore volumes in our materials and make them more fragile. Therefore, iron powders can be used as a pore-forming agent in the synthesis of porous Mbo-based PIPs and as fillers for MaJ based PIPs.