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Silica extracted from rice husk, which is represented as SRH, is inexpensive mesoporous silica useful for heavy metal removal from industrial waste effluents. SRH was synthesized through calcination at 650°C in an oxidant atmosphere obtaining a mesoporous silica with BET area of 297 m 2 g-1 and 2.3 nm of pore diameter average, respectively. The surface of this silica was modified through a post-synthesis route with amine and polyamine groups obtained at 16% and 47% of modified surface with amine or polyamine groups (SRH-NH 2 and SRH-triamine). The chromium(III) removal capacity of SRH and amine-modified silica was tested with stock solutions, observing a fast sorption process and reaching its equilibrium adsorption time in 20 min. The resulting Cr(III) removal capacity was 6.7, 22.1 and 34.3 mg g-1 for SRH, SRH-NH 2 and SRH-triamine silicas, respectively. SRH and SRH amine silicas were used to remove Cr(III) from a sample taken from a tannery waste effluent from the city of Leon, Guanajuato, Mexico, and displayed a 70% and 90% removal, respectively. Our results confirm the ability of these inexpensive silicas to adsorb materials and their potential use in heavy metals removal processes from industrial waste effluents.

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The pharmaceutical industry has seen an increased need of carriers or excipients design that allows the controlled release of a drug in the human body. The main role of an excipient is to carry the drug for its administration under therapeutic index. Among the new generation of excipients, the ordered mesoporous silica (MS) presents several advantages, such as excellent biocompatibility, good adsorption capacity, and precise control in the drug delivery. However, the high cost of synthesis of mesoporous silica restricts its use to industrial applications; therefore, a low-cost procedure is necessary for widespread use. Biogenic silica from rice husk (SiO 2 -rice) could be a new choice as a drug delivery system. This silica is obtained from an acid leaching of rice husk followed by calcinations processes at low temperatures; these conditions produce silica with good adsorption properties, similar to those of MS. In consequence, the excipient behavior of SiO 2 -rice was assessed using folic acid as the model drug, displaying an 18.5% of absorption in the SiO 2 -rice pores, while MS absorbed around 19%. The drug release profiles were similar for both the silicas, suggesting that SiO 2 -rice could be a low-cost, similar yield excipient for drugs similar to folic acid.

The processing of refractory minerals of gold and / or silver occluded in quartz in sizes less than 1 μm is not viable, due to the chemical inertness of the silica. The treatment of these minerals is usually carried out by reduction of particle size by fine grinding that allows the release of the occluded particles. As an alternative to processing these minerals, has proposed the partial dissolution of the silica with diols in basic medium; in these studies partial dissolution of the matrix has been observed in 25% with triisopropanolamine and 3% mol KOH. The present work shows the effect of the type of base (organic-amines) in the dissolution of the matrix, observing a greater dissolution with the basic character of these and with the chelating effect of the same ones. Et3N was the weak base that showed the highest dissolution of the matrix, observing a dissolution rate (0.67 mmolmin-1) 2.5 times lower than that observed with KOH (1.66 mmolmin-1), similarly the observed effective diffusion coefficient was of an order of magnitude lower than that observed with KOH.