Removal of lead from aqueous solutions by using nanoporous silica materials obtained from wheat husk biosilica

Various technological innovations came into our lives with the rapid development of the industry and serious environmental pollution occurred as a result of industrialization which is incontrovertible. The heavy metal pollution poses a serious problem for health that is a current problem in terms of environmental pollution. The heavy metals in industrial waste water are deposited especially by water and soil, blending by plants and animals and then leads to health problems in people by participating to the food chain. The adsorption method is widely preferred for heavy metal removal due to being inexpensive and easy. The evaluation of wastes is an important issue depending on the sustainable development of the existing strategy on the agenda of European Union countries and many others. The evaluation of waste materilas by reusing or recycling to produce materials is located primarily. The other evaluation methods are using the wastes in energy field and if possible disposal them with the ecologically advantageous methods. In another aspect, gradually increasing ash wastes leads to global warming and environmental pollution. Therefore, evaluation of agricultural waste ashes and investigation the chemistry in order to determine the properties of ashes is one of the current topics to be addressed by the scientific community. Wheat is a major crop product. Dehusking results in large quantities of the wheat husk that is generally burned and produces a solid waste – the wheat husk ash. Most of the times, the ashes are either dumped or left to their fate, thus one way or another it can cause pollution. Ashes consist of amorphous silica that can be used to synthesize the silica-based materials. The current study aimed to utilize agricultural waste, wheat husk to produce nanoporous silica materials as zeolite NaA and silica aerogel for the first time to use for the adsorption of lead ions from aqueous solutions. The silica is extracted from the raw material, wheat husk that was leached by acid. The effect of production conditions on the surface and physical properties of adsorbents obtained from wheat husk silica were investigated and discussed based on the results obtained by means of various techniques including N2 adsorption, Fourier transform infrared, X-ray diffraction, scanning electron microscope and energy dispersive X-ray. The influence of adsorbent dose, initial lead concentration, pH, temperature and time on lead removal from aqueous solutions by use of nano-porous silica materials were evaluated in the batch system. The lead removal by zeolite NaA was evaluated statistically using the Box-Behnken method. The adsorption conditions were optimized, and the mechanisms of adsorption are determined. Equilibrium adsorption data were applied to Langmuir, Freundlich, and Dubinin Radushkevich adsorption model. Regeneration of zeolite NaA and silica aerogel samples were carried out by using different strength of salt and acid solutions, respectively. The pore size and surface area of nanoporous silica materials were ranged between 3.26-45.75 nm and 0.48-328.88 m2 g-1, respectively. Maximum Pb(II) removal was obtained at pH 5.5. The polynomial (quadratic) model provided the best fit to experimental data were for all adsorbents. Consequently, zeolite NaA and silica aerogel were found to be effective adsorbents to remove lead Pb(II).