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Rice husk ash (RHA) is a waste material produced in large quantities in many regions worldwide, and its disposal can be problematic. This work describes a method for using RHA to synthesize silicon and potassium slow-release fertilizer. The extraction of silica from RHA was accomplished by alkaline leaching with KOH. Different KOH concentrations and reaction times were evaluated and the best production of K 2 SiO 3 solution was achieved using 6 mol L -1 and 6 h, respectively. The fertilizer was synthesized by the reaction of K 2 SiO 3 with KAlO 2 in aqueous medium, followed by calcination at 500 °C. X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses indicated that the fertilizer composition was similar to mineral kalsilite. Solubility essays indicated lower K + and Si 4+ release percentage in neutral medium. Kinetic mechanisms of release tests can be well explained by the pseudo-second order model. The proposed synthesis seems to be a viable process offering economic and environmental benefits.Keywords: rice husk ash, silicon, potassium, slow-release fertilizer IntroductionNowadays, one of the most important goal of agronomic management is the development of environmentalfriendly fertilizers, which promote a sustainable nutrient management to ensure growth crop yield.1 One method of reducing fertilizer nutrient losses involves the use of slowrelease fertilizers, which have been designed to gradually release nutrients to plants at a rate to coincide with the requirement of crops. The advantages of using slow-release fertilizers instead of the conventional type are various, such as the increased efficiency of the fertilizer, the continuous supply of nutrients for a prolonged period and a decrease of nutrient losses by volatilization and leaching out to surface and ground water. 2,3 Potassium (K) is known as one of the most required nutrient during plant growth. K plays an important role in the energy state of the plant, translocation and storage of assimilates and maintenance of water in plant tissues. 4 For many crops, silicon (Si) is also an important nutrient and its availability to plants is often associated to increase of crop yield. 5Plants under intensive cultivation that require high absorption of Si, such as rice, sugar cane, and grasses in general, can quickly deplete the soluble Si content of soil. This element, therefore, needs to be replaced by fertilization. The application of Si fertilizer can influence plants in two ways: (i) by improvement of the fertility and chemical properties of the soil, and (ii) by direct effects on plant growth and development.6 Positive effects that have been reported include improved plant structure, such as upright leaves and stems, 7 and increased resistance to fungi and insects due to deposition of Si under the plant cuticle. 8 The high Si content of rice husk ash (RHA) has led to interest in its use as a source of Si for plants and for the production of numerous Si-based materials.9 RHA is generated after burning the rice husk, which is a waste from the ric...

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A novel oilwell cement slurry was prepared with in situ polymerized epoxidized A/F bisphenol–chitosan and characterized by 29Si NMR and EPR spectroscopy. The hydrated and cured cement slurry evidenced the presence of unreacted clinker phases identified by the presence of orthosilicate groups along with the presence of hydration products identified by short linear polymeric silicate units typical of calcium silicate hydrate (CSH). Two main Fe3+ domains and Mn2+‐related hyperfine sextets were detected by EPR spectroscopy. After long‐term contact with an API acidizing fluid, the features of the 29Si NMR and EPR spectra did not change appreciably. The kinetics of overall solids dissolution upon contact with the hot acidizing fluid was modeled with the Avrami‐Erofe'ev equation. The kinetic parameters are not very sensitive to changes of temperature. The values of the Avrami exponent suggest that diffusion‐controlled processes without chemical reactions govern the overall rate of interaction processes or are partially involved in it. The results indicate that the A/F bisphenol–chitosan polymeric network can improve significantly the chemical stability of cement slurries in the presence of acidizing fluids and may be a good option for oil and gas industry. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41044.