Chemical And Mineral Analysis Of Raw And Acid-Treated Clays From Kano Plains, Kisumu County, Kenya

ABSTRACT

Clays are aluminosilicate minerals which are widely spread in the earth’s crust. They also naturally contain iron because of its high relative abundance of about 6.5% .They have many applications such as, use in manufacture of Portland Cement, ceramic products such as bricks, roofing tiles and high quality ceramic products as crockery. For the manufacture of high quality ceramic products, the level of iron in the clays should not exceed 1%. This study was done on clays of Kano plains, Kisumu County, Kenya to find out the elemental and mineral composition of the clays with special interest on levels of iron since it affected clays’ use in making high quality ceramics. Further investigation was done on whether iron levels, if found to be high, would be lowered by mineral acids of different concentrations at different temperatures to improve clay quality for manufacture of high quality ceramics. Powdered raw clay samples dried at 105oC for six hours in a desiccator, digested or pelleted were analysed by AAS, EDTA titrations and XRF for elemental composition, and by XRD and IR for mineral composition. The samples were then treated with mineral acids of different concentrations at room and boiling temperatures for 12 hours to remove as much iron as possible and the residual clay washed, dried and analysed for Fe, Al and Si contents. The percentage elemental composition for the raw clays by AAS were expressed as oxides and ranges of identified elements found to be 45.47±0.18 to 64.70±0.10 SiO2, 12.54±0.37 to17.95±0.19 Al2O3, 3.74±0.08 to 10.28±0.06Fe2O3, 0.44±0.01 to 1.17±0.01MgO, 0.56±0.02 to 2.34±0.01CaO, 2.07±0.013 to 11±0.08 K2O, 0.98±0.1 to 1.86±0.01 Na2O, 0.92±0.02 to 2.49±0.01 TiO2, 0.02±0.01 to 0.25±0.01 MnO and LOI of 9.77±0.15 to 15.40±0.10. The minerals in the raw clays, identified by XRD included Montmorillonite (Ca,Na))0.3Al2(Si,Al)4O10(OH)2.xH2O, Kaolinite Al2Si2O5(OH)4, muscovite, KAl2(Si3Al)O10(OH,F)2, Albite, Na(AlSi3O8), Orthoclase KAlSi3O8 and Dickite Al2(Si2O6(OH)4. Acid-treated clays gave different mineral composition and saw Montmorillonite, Kaolinite, Muscovite and Quarts detected in raw samples disappearing completely, and Ilmenite (Ni.25Mn.25Zn.25Mg.25)TiO3 and (Ni.5Mn.5)TiO3), the titanium ore, Microcline KAlSi3O8 and Calcite, CaCO3, emerging after acid-treatment. The findings showed levels of iron reduced by minerals acids from average 8.25% to less than 1% achieved by boiling clays with 6-8 M sulphuric acid. The levels of aluminium were lowered sparingly from 15.9% to 13.7% while levels of silicon remained unchanged. Second finding was that acid treatment alters mineral composition and cause interconversion of the clay minerals. Further, mineral composition given by chemical formulae showed that iron in the clays was not in the mineral structure and existed as an accessory component. The findings led to the conclusion that iron levels in raw clays were high but were lowered to less than 1% by mineral acids which improved their quality for making high quality ceramics. Data analysis was done by SPSS software.