Iranian journal of chemical engineering
Volume:4 Issue: 1, winter 2007

The ternary system of Portland cement-microsilica-limestone has been studied by investigating its set and strength behaviours. A number of different cementitious systems comprised of 0, 10, 15, 20, 25, and 30% limestone powder and 0, 4, 6, 8, 10, 12, 14, and 16% microsilica were designed and prepared. The cementitious systems were then characterized by determining their relative workability and measuring their initial and final setting times and also their 7- and 28-day compressive strengths using paste specimens prepared at a constant W/C-ratio of 0.38. Total 77-day shrinkage of the systems was also measured. The obtained results reveal that both 7- and 28-day compressive strengths increase with increasing microsilica up to 12% and decrease with increasing the percentage of limestone powder. A comparison of the results confirms the possibility of replacing Portland cement by a proportioned mixture of microsilica and limestone powder for enhancing the strength behaviour or producing composite cements containing relatively high proportions of limestone powder with no loss in 7- and 28-day compressive strengths compared to plain cement.

Heterogeneous photocatalytic degradation of Polynuclear Aromatic Hydrocarbons (PAHs) contaminated soil in the Pars Economic and Energy Zone was carried out under laboratory conditions to evaluate the potential use of this technology for in situ remediation. Analysis of soil samples show that contaminated soil is primarily related to the concentration of phenanthrene. Hence phenanthrene is used for photocatalytic degradation under laboratory conditions. Soil samples were spiked with two phenanthrene concentrations (50 and 100 mg kg-1), loaded with catalyst TiO2 and exposed to uv light with 125 W power. Different catalyst loads (1, 2, 3 and 4 % w/w) were tested in phenanthrene contaminated soil (50 mg kg-1) for up to 16h exposure. Both the catalyst and phenanthrene concentration show no influence on the kinetics of the phenanthrene degradation. The results indicated that the optimum removal condition was at 2% w/w catalyst and 100% w/w water with 85% degradation efficiency. The degradation efficiency of other PAHs was also assessed with the optimum condition. This paper shows that photocatalytic is a particularly important methodology, in which a major process is being made in the oxidative methods for the degradation of organics such as PAHs in contaminated soil.

Activated carbons are extremely versatile adsorbents for major industrial significance, especially for metal ions recovery from wastewaters. In this study, the activated carbon prepared from the hard shell of apricot stones, an agricultural solid, which was used for the gold recovery from gold-plating wastewater is investigated. Activated carbon was produced by chemical activation with phosphoric acid. Recovery parameters such as adsorbent dose, the particle size of the activated adsorbent, pH and the agitation speed of mixing were studied. The equilibrium data fit well with the Freundlich isotherm model. A Langmuir isotherm model has been used to obtain thermodynamic parameters. The results showed that under the optimum operating conditions, more than 98 per cent of the gold was recovered by activated carbon after only 3 hours. It was found that the activated hard shell of apricot stones could be used as an effective adsorbent for gold recovery from wastewaters.

Carbon black or soot is a carbon rich material which is widely used as a modifier and filler. Usually carbon black is produced via thermal decomposition of heavy hydrocarbons. This process is too complex to be modelled fundamentally. In this study, the effect of reaction feed composition on the soot production yield was studied experimentally in a lab-scale reactor. The soot production was optimized based on feed Composition and economical aspects. The effects of reaction time and temperature on the product particle size produced using the optimized feed were also investigated experimentally. Then a semi-empirical model was developed to predict soot particle size as a function of reaction time and temperature. The model has been validated upon the experimental data successfully.

This investigation was designed to evaluate the effects of bioaugmentation on maintaining the system stability under shock loading conditions, standardizing the effluent, and improving the sludge settlement. In this study, phenol was chosen as a model of mono-aromatic compounds which are found commonly in many industrial wastewaters, especially petroleum refineries and the petrochemical industry in Iran. Impacts of bioaugmentation with the best isolated microorganism on the system performance facing sudden toxic shock were investigated after acclimatizing the system with phenol, isolating the phenol degrading microorganisms, and selecting the best phenol degrading strain. Results indicated that this method was improved the efficiency of the system under shock loading from 30% to 94% and SVI from 333 ml/g to 80 ml/g. The effluent was standardized after bioaugmentation at a minimum HRTs of 10, 10, 12 and 24 h, respectively, and at influent COD of 800, 1000, 1500 and 2000 mg/l. The system efficiency and SVI were located in an average range of 99.4-99.9% and 50-71 ml/g, respectively, and the sludge growth was good, even under high organic loading rates after bioaugmentation. In conclusion, bioaugmentation could be used as an effective and efficient method to improve a CAS process facing sudden toxic pollutant shock loading.

Secondary growth technique was successfully applied for the synthesis of nanostructure sodalite membranes with vacuum seeding on tubular α-Al2O3 supports. In the seeding process, a thin, uniform and continuous seeding layer was closely attached to the support external surface by the pressure difference between the two sides of the support wall. The final nanostructure sodalite top-layers were synthesized on the seeded support into a stainless steel autoclave with a Teflon holder. The effect of seeding time on the microstructure of the synthesized sodalite top-layers was investigated at four different levels 60, 120, 180 and 240 s. The synthesized membranes were characterized by XRD, SEM and mercury porosimetry. The obtained results showed that sodalite zeolite was synthesized on the membranes top-layers with uniform surfaces. But, the top-layers thickness increases by increasing the seeding time and tends to reach a plateau. Further increasing the seeding time causes dense top-layers to form. Also, the performance of the manufactured sodalite membranes was evaluated by permeations of single gases (H2 and N2) under different pressure differences at a temperature of 283K. It is found that the membrane permeance shows a maximum value at seeding time 180 s with a constant permselectivity (H2/N2) of about 2.5. The permeation results were confirmed by SEM micrographs which showed a thick and low-dense top-layer in the membranes manufactured with the seeding time of 180 s.