Green Chemistry Preparation and Characterization of Rice Husk Derived Silica Gel in Kenya

Rice is a grass seed from Oryza glaberrima species also known as the African rice.In Kenya,rice is mostly grown in Central(Mwea)and Nyanza(Ahero,West Kano,Migori and Kuria)areas.Milling rice produces rice husks as by-products which can be sources of valuable chemical products(silica gel,sodium silicate).In trials to produce silica gel from rice husks,rice husks were charred in a combustion chamber(30 min)then ashed in a Muffle furnace(Advantec KL-420)at different temperatures.The ashes were then leached with distilled water/acids to remove metal oxides.Sixty grams(60 g)of the leached RHA(Rice Husk Ash)was mixed with 300 mL of 3 M NaOH solution in a Pyrex 500 mL beaker and boiled at 100℃(1 h).The silica gel samples were characterized using several methods.Elemental analysis was done using TXRF(Total X-Ray Fluorescence),while FTIR(Fourier-Transform Infrared Spectroscopy)was used to obtain an infrared spectrum of absorption of the silica sample.Results of the analysis conform to local and international quality standards.The rice husks had an average moisture content of 7.07%and 1.00-2.00 mm diameter.And 1.74%of the rice husk had pore sizes of about 0.710 mm.The average ash content was 22.65%.At 600℃,leaching with water yielded 98.2%silica compared with 99.1%(H2SO4)and 96.9%(HCl).At 500℃,leaching with HCl/H2SO4 causes a decrease.At 500℃,the availability of SiO2 is more for water leached samples.At 400℃,water leaching gave 98.49%silica while HCl leaching was 97.85%silica and H2SO4 was 99.41%.Silica is a precursor of silica gel.Statistical analyses imply water leaching RHA instead of acid leaching at 500℃ will produce a significant amount of silica gel.The open burn samples produced equal or better SiO2(silica gel precursor)yields compared with the incineration samples.FTIR analysis of the silica gel sample compared well with adsorption peaks of silica gel in literature.XRD(X-Ray Diffraction)analysis produced a pattern consistent with other XRD patterns of silica gel published by other researchers.

Development of Novel Products from Agro-Wastes(Rice Husks)and Characterization in Kenya

Rice growing is a popular agricultural activity in some areas in Kenya.The challenge is in the disposal of RH(Rice Husks).Rice production results in 20%RH as byproduct.Simple incineration of RH results in RH ash which is a source of valuable chemical products.The ash is 87-97%silica,highly porous and light weight,with a very high external surface area.The end product of RHA(Rice Husk Ash)after chemical treatment,sodium silicate,is a precious commodity that has myriad applications especially in detergent manufacture and soap production.The objective was to determine the best conditions to synthesize silica from agro-wastes(RH)in Kenya.The yield(%SiO2)of the HCl(Hydrochloric Acid)leached RH at 500°C was the highest at 99.2%.Overall these conditions were the best in producing silicate.Percentage(%)removal of each metal is different due to its chemical form in RH.The removal percentage of K is especially remarkable.And 0.5 M HCl leaching followed by thermal treatment of 600°C gave the best increase in%silica dioxide.The same process removed the most metallic impurities(P2O5,K2O,CaO,Mn and Zn).Leaching with 0.5 M HCl followed with thermal treatment of 500°C gave the best overall yield in%silica dioxide.An increase in temperature from 600°C slightly reduced the%silica dioxide content.The 0.5 M HCl used in these trials was able to produce 99.17%silica content from the Mwea RH.The SiO2 obtained with the water washed RH sample is 97.37%as compared 99.17%(HCl-washed)and 99.02%(H2SO4(Sulphuric Acid)-leached).The FTIR(Fourier Transform Infrared Spectroscopy)spectra indicates HCl leaching avails more silica content than H2SO4 leaching.

Elemental Analysis of Fly and Bottom Ash from Burners/Incinerators in Selected Health Care Facilities in Kiambu County, Kenya

Medical waste incinerators emit a wide range of pollutants like heavy metals, dioxins and furans. These include Pb （lead）, Hg （mercury）, Cd （cadmium）, fine dust particles and PICs （products of incomplete combustion）. The objective was to determine the elemental composition of medical waste residue after incineration in selected hospitals in Kiambu County, Kenya. Bottom/fly ash samples were collected from the burners/incinerators in the selected health care facilities visited. The concentrations of the metals in the fly ash and bottom ash were determined using an XRF （X-ray fluorescence） spectrometer after acid digestion. The concentrations of heavy metals in the fly and bottom ash were as follows： Ti （titanium） 62-839 mg·kg^-1 and a mean of 202 mg·kg^-1 and 344 mg·kg^-1 in fly ash and bottom ash, respectively. Ca （calcium） was 37,753-204,475 mg.kg1 with means of 27,132 mg.kg-1 in fly ash and 131,185 mgg·kg^-1 in bottom ash. Zn （zinc） was 297-6,605 mg·kg^-1 with means （2,307 mg·kg^-1 in fly ash, 4,359 mg·kg^-1 in bottom ash）, Pb （13-1,819 mg·kg^-1） had means of 280 mg·kg^-1 in fly ash and 291 mg-kg-1 in bottom ash. Cu （copper） （9.5-250 mg·kg^-1） had means of 83.47 mg·kg^-1 in fly ash and 98.8 mg·kg^-1 in bottom ash. The wide variations in results can be attributed to the different burners/incinerators used and different segregation methods of the medical waste. The results show that the reported levels of heavy metals could pose a health risk due to possible leaching after disposal.