Caractérisation minéralogique et géochimique des scories volcaniques de la ligne du Cameroun en vue de leur utilisation comme matière première dans la fabrication du ciment

Abstract

The study was carried out on volcanic scoriae from nine localities on the southern mainland of the Cameroon Volcanic Line. It aimed to evaluate their characteristics in accordance with the requirements required for applications in the cement industry. The study of the volcanic scoriae was done through an approach whose elements are made up from the sampling sites to the laboratory. The laboratory investigations consisted of petrographic, mineralogical and geochemical characterization followed by an evaluation of physico- technical parameters. The volcanic scoriae consist of pyroxene and olivine phenocrystals that bathe in a mesostasis made of plagioclase microlites, which gives them a porphyric microlitic texture. The weathering minerals present in the mineralogical cortege are kaolinite, illite, montmorillonite, ettringite, portlandite and hematite. The minerals identified are characterized by O-H, Si-O-Si, Al-O-Si functional groups that attest to the coexistence of the crystalline and amorphous phases. The chemical composition of slag is dominated by three major oxides (SiO2, Al2O3 and Fe2O3). The TAS diagram classified these volcanic scoriae into picrobasalt, basalt, hawaiite and basanite. These rocks are rich in lithophilic elements corresponding to the most abundant trace elements. The concentrations of transition elements indicate that the partial melting of the mantle would be at the origin of the genesis of volcanic scoriae. The high LREE/HREE ratio indicates a predominance of light rare earths. The elementary ratios (La/Yb, Tb/Yb and La/Sm) show that these materials come from garnet peridotite. The effect of meteoric alteration is marked by the presence of iddingsite, an index of mafic alteration varying from 28 to 51%. Illite and montmorillonite indicate that the chemical alteration would have been moderate. Thermogravimetric analysis showed a thermal behavior that highlights the coexistence of crystalline and amorphous phases. The high contents of the amorphous phase (10 - 70%) in the volcanic scoriae correspond to those of aluminosilicate materials. Pozzolanic properties such as pozzolanicity index (65 to 90%) and compressive strength (21-47 MPa) with values within the range of those of common concretes attest to sufficient to very good pozzolanic activity for the volcanic scoriae studied.