Dissolution kinetics of synthetic zeolite NaP1 and its implication to zeolite treatment of contaminated waters

A Study of Using Natural Sorbent to Reduce Iron Cations from Aqueous Solutions

Iron is an essential trace element, but at high doses, this element may pose a health risk. Wastewater from iron ore mining, steel production, and metal processing, among other heavy metals, also contains high concentrations of iron (Fe3+). The use of sorption on natural materials is a potential alternative to conventional methods for removing iron ions, also because of low cost. The methods presented in this article are based on the study of kinetic properties and the acquisition of adsorption isotherms, which are one of the most important characteristics of adsorption mechanisms. The course of sorption is analyzed according to the Freundlich sorption isotherm model. Isotherm parameters are evaluated using experimental results of ferric cation sorption. The results presented relate to the investigation of natural zeolite-clinoptilolite as a ferric cation sorbent, providing a measurement of the sorption kinetics as well as the observed sorption parameters of iron cations from aqueous media. The optimal time for equilibrium in the adsorption system is determined from the kinetic dependencies. The dependence of the achieved equilibrium concentration on the initial concentration of the solution was also expressed, both graphically and analytically. The new prediction model was compared with the traditional Freundlich model. Finally, adsorption isotherms tested under laboratory conditions for a practical application can be recommended for the preliminary examination of the possible technological use of natural zeolite in the wastewater treatment process.

Efficient method for recycling silica materials from waste powder of the photonic industry

An efficient and economic approach is proposed for the fast and direct recovery of silica materials from photonic waste powder. Unlike the conventional alkaline fusion method for the extraction of silica from waste materials, this method possesses advantages of a rapid and low-energy-consumed process with total recovery yield. The obtained mesoporous silica material, denoted as MCM-41(DU)-F, was recovered directly from photonic waste powder at room temperature with the assistance of cationic surfactant, hydrofluoric acid, and ammonia hydroxide. The recycled MCM-41(DU)-F with a high specific surface area (788 m(2)/g), ordered mesoporous structure (4.5 nm), and large pore volume (1.1 cm(3)/g) was used as support of tetraethylenepentamine (TEPA) for the capture of CO2 from a flue gas stream. The results demonstrated that TEPA-impregnated MCM-41(DU)-F had an adsorption capacity of 120 mg of CO2/g of adsorbent. This is higher than the amount adsorbed by TEPA-MCM-41(NaSi) made from pure chemicals (113 mg of CO2/g of adsorbent) and TEPA-MCM-41(AF) made from alkaline fusion (112 mg of CO2/g of adsorbent) under the same testing conditions. This novel recycling process, which can improve cost effectiveness for the mass production of valuable mesoporous silica materials from cheap and abundant resources through convenient preparation steps, is surely beneficial from the viewpoint of economical use of photonic industrial waste powder.

Mineral sequestration of CO(2) by aqueous carbonation of coal combustion fly-ash

The increasing CO(2) concentration in the Earth's atmosphere, mainly caused by fossil fuel combustion, has led to concerns about global warming. A technology that could possibly contribute to reducing carbon dioxide emissions is the in-situ mineral sequestration (long term geological storage) or the ex-situ mineral sequestration (controlled industrial reactors) of CO(2). In the present study, we propose to use coal combustion fly-ash, an industrial waste that contains about 4.1 wt.% of lime (CaO), to sequester carbon dioxide by aqueous carbonation. The carbonation reaction was carried out in two successive chemical reactions, first, the irreversible hydration of lime. second, the spontaneous carbonation of calcium hydroxide suspension. A significant CaO-CaCO(3) chemical transformation (approximately 82% of carbonation efficiency) was estimated by pressure-mass balance after 2h of reaction at 30 degrees C. In addition, the qualitative comparison of X-ray diffraction spectra for reactants and products revealed a complete CaO-CaCO(3) conversion. The carbonation efficiency of CaO was independent on the initial pressure of CO(2) (10, 20, 30 and 40 bar) and it was not significantly affected by reaction temperature (room temperature "20-25", 30 and 60 degrees C) and by fly-ash dose (50, 100, 150 g). The kinetic data demonstrated that the initial rate of CO(2) transfer was enhanced by carbonation process for our experiments. The precipitate calcium carbonate was characterized by isolated micrometric particles and micrometric agglomerates of calcite (SEM observations). Finally, the geochemical modelling using PHREEQC software indicated that the final solutions (i.e. after reaction) are supersaturated with respect to calcium carbonate (0.7 < or = saturation index < or = 1.1). This experimental study demonstrates that 1 ton of fly-ash could sequester up to 26 kg of CO(2), i.e. 38.18 ton of fly-ash per ton of CO(2) sequestered. This confirms the possibility to use this alkaline residue for CO(2) mitigation.