The processes used to remove heavy metals from inorganic wastewater have in general low efficiency. The use of activated peat obtained by using a process similar to a cation exchange reaction increases the removal efficiency up to five times when compared with peat “in natura”. The main objective of this work is to show the fundamental mathematical model, governed by diffusion process and the algorithms utilized to design the batch and the continuous feed stirred tank reactors or in some cases a fixed bed reactor. The principal dimensions of these equipments are obtained from the knowledge of the activated peat's cation exchange capacity used in the process, and the main chemical characteristics of the heavy metal ion contained in the wastewater. Besides, two important parameters are also included: the ion concentration and the efficiency of the process obtained from laboratory kinetics experiments. For example Pb+2 is removed l:rom a wastewater at a concentration of 50g/m3 in five minutes or less, with an efficiency of 98%.
A flow injection analysis (FIA) system com-prising a tartrate-(TAT) selective electrode has been de-veloped for determination of tartaric acid in wines. Sev-eral electrodes constructed for this purpose had a PVC membrane with a complex of quaternary ammonium and TAT as anion exchanger, a phenol derivative as additive, and a more or less polar mediator solvent. Characterization of the electrodes showed behavior was best for membranes with o-nitrophenyl octyl ether as solvent. On injection of 500 L into a phosphate buffer carrier (pH = 3.1; ionic strength 10 -2 mol/L) flowing at 3 mL/min, the slope was 58.06 ± 0.6 with a lower limit of linear range of 5.0 10 -4 mol/L TAT and R 2 = 0.9989. The interference of several species, e.g. chloride, bromide, iodide, nitrate, gallic acid, tannin, sucrose, glucose, fructose, acetate, and citrate, was evaluated in terms of potentiometric selectivity coefficients. The Hofmeister series was followed for inorganic species and the most interfering organic ion was citrate. When red and white wines were analyzed and the results compared with those from an independent method they were found to be accurate, with relative standard deviations below 5.0%.
This work investigates the deposition of Pt nanoparticles onto carbon aerogels (CA), derived from microcrystalline cellulose. Nanoparticles are synthesised via impregnating the CA with H 2 PtCl 6 followed by reduction either under H 2 at 300 C or in a basic NaBH 4 solution. H 2 reduction yields uniform Pt nanoparticles (average diameter < 2nm) dispersed over the CA surface as revealed by Transmission electron microscopy (TEM). Larger agglomerates can be seen in TEM images of NaBH 4 reduced samples, which is confirmed by powder X-ray diffraction (XRD). A rotating disk electrode was employed to analyse the electrochemical properties of the Pt nanoparticles. The active area of the platinum nanoparticles was evaluated using hydrogen adsorption/desorption cyclic voltammetry and CO stripping measurements. The oxygen reduction reaction was also studied to (i) obtain the kinetic parameters of oxygen reduction for the Pt/CA materials and (ii) compare them with commercial Pt/Carbon Black.
The reduction of the heavy metals concentration in liquid effluents is difficult and the existing methods available are expensive and their efficiencies ate in general low. The normal procedure adopted is based on the recirculation of the “chorume”, sometimes with a high content of heavy metals, into the liquid effluent flux of the central processing unit having in general a biological treatment. Depending on the heavy metal concentration the efficiency of the biological process decreases, or in certain cases, collapses completely. Activated peat by using the acid process or the one developed by the Universidade Federal de Sergipe and Instituto de Tecnologia e Pesquisas de Sergipe becomes an excellent heavy metals sorbent, which in certain analytical conditions has a very high efficiency. The overall process is controlled by diffusion and is governed by a first order kinetics. The use of activated peat shows in several situations that this process is a feasible alternative to getting the reduction of heavy metals concentrations in simulated effluents with one or more cations. Preliminary results show a significant matrix influence. The organic matter presence in the effluent may alter the sorption efficiency depending on its composition. The optimum analytical condition varies with the effluent quality and promotes the highest efficiency in the reduction of heavy metals concentrations.
Smectite clays or bentonites are used in several industrial applications. The aim of this study was to describe the characterization and organophilization of a green clay sample coming from the State of Paraíba, Brazil. The clay was characterized by XRD, XRF, CEC, SEM, stereoscopic microscopy, Fann viscosity (before and after the organophilization process), swelling capacity in water and some organic solvents. Prismatic specimens were conformed by pressing, for which were conformed the mechanical sthegth after drying at 110°C and after burning at 950°C. The burned specimens were analyzed to evaluate dimensional variations, water absorption, apparent porosity and apparent density. XRD showed that the sample was constituted mainly for montmorillonite claymineral. Analysis of rheological properties of the modified clay indicates its potential to meet the specifications of the standard N-2604 of Petrobras, concerning clays used to oil drilling.
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