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Pressure oxidation of pyrite-arsenopyrite refractory gold concentrate

Rusanen L., Aromaa J., Forsen O.

Physicochemical Problems of Mineral Processing

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2013

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Vol. 49, iss. 1

101--109

EN

Refractory gold ores have poor gold recoveries with direct cyanide leaching. Typically the refractoriness is due to encapsulation of the gold particles inside the host mineral. To liberate gold for leaching the host mineral must be broken by mechanical or chemical means. The aim of this study was to study the effect of temperature, oxygen partial pressure and slurry density on pressure oxidation of pyrite-arsenopyrite gold concentrate. Batch oxidation tests in an autoclave were done using a factorial design. Different responses were measured and analysed to study effect of the three factors and oxidation kinet-ics. Generally, high slurry density required high temperature and oxygen partial pressure to reach com-plete oxidation. Oxidation kinetics at 225°C temperature, with 1050 kPa oxygen partial pressure and 15% slurry density was found to be fastest resulting in complete conversion of sulfides in 30 minutes. At 195°C, 700 kPa oxygen partial pressure and 10% slurry density, the oxidation kinetics for complete sul-fide conversion was about 60 minutes. Slurry densities above 10% had an adverse effect on the oxidation rate, when the temperature was below 225°C and oxygen partial pressure below 1050 kPa.

2

Optimization and equilibrium studies of Pb(II) removal by Grewia Asiatica seed: a factorial design approach

Siyal A. N., Memon S. Q., Khaskheli M. I.

Polish Journal of Chemical Technology

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2012

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Vol. 14, nr 1

71-77

EN

This study aims to explore the efficiency of an agro waste material for the remediation of Pb(II) contaminated water. A factorial design approach is adopted to optimize removal efficiency and to study the interaction between effective variables. A face-centered Draper-Lin composite design predicted 100% removal efficiency at optimum variables; pH 8, initial concentration of Pb(II) ion 12mg/L, sorbent dose 200mg and agitation time 110 min. Regration coefficient (R2 = 99.9%) of a plot of the predicted versus the observed values and p value (>0.05) confirms the applicability of the predicted model. Langmuir and Dubinin-Radushkevich (D-R) isotherm models were applicable to sorption data with the Langmuir sorption capacity of 21.61š0.78 mg/g. The energy of sorption was found to be 13.62š0.32 kJ/mol expected for ion-exchange or chemisorption nature of sorption process. Characterization of Grewia seed suggested a possible contribution of carboxyl and hydroxyl groups in the process of biosorption. The present study shows that Grewia seeds can be used effectively for the remediation of Pb(II) contaminated water.

3

Novel Calix[4]arene network resin for Cr(VI) ions Remediation : A Response Surface Approach

Siyal A. N., Memon S. Q.

Polish Journal of Chemical Technology

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2012

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Vol. 14, nr 3

21-28

EN

Novel Calix[4]arene Netwok (NCN) resin has been synthesized using Amberlite XAD-2 as the starting material. Hydroxyl groups have been introduced onto the para position of alkylated phenyl ring of Amberlite XAD-2 followed by the condensation to NCN by reacting it with formaldehyde. The NCN resin has been used for the remediation of Cr(VI) contaminated water using factorial design approach. A face-centered Draper-Lin composite design predicted ~100% removal effi ciency at optimum variables (the initial concentration of Cr(VI) ion 10 mg/l sorbent dose 200 mg, agitation time 136 min and pH 2). The accuracy and the fi tting of the model were evaluated by ANOVA and R2 (0.9992) values. The 99.5% removal effi ciency has been achieved experimentally at the optimum values of the variables. The Langmuir and D-R isotherm models were applicable to the sorption data with the value of RL and the sorption free energy 0.0057-0.1 and 7.93 kJ/mol respectively, suggesting favorable and physical/ion-exchange nature of the sorption. The calculated sorption capacity was 176.1š2.4 mg/g. The recycling studies of NCN resin showed that the multiple use of resin is feasible. Effect of concomitants has also been studies and proposed method was applied successfully for removal (98.7%) of Cr (VI) from electroplating wastewater.

4

Process optimization of nickel extraction from hazardous waste

Gharabaghi M., Irannajad M., Azadmehr A. R., Majid E.

Archives of Environmental Protection

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2012

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Vol. 38, no. 3

29-40

EN

Zinc plant residue is a hazardous waste which contains high quantity of nickel and other valuable metals. Process parameters such as reaction time, acid concentration, solid-liquid ratio, particle size, stirring speed and temperature for nickel extraction from this waste were optimized using factorial design. Main effects and their interactions were obtained by the analysis of variance ANOVA. Empirical regression model was obtained and used to predict nickel extraction with satisfactory results and to describe the relationship between the predicted results and the experiment results. The important parameters for maximizing nickel extraction were identifi ed to be a leaching time solid-liquid ratio and acid concentration. It was found that above 90% of nickel could be extracted in optimum conditions

5

Development and validation of a selective method for the determination of chrysene using silver-enhanced room-temperature phosphorimetry

da Cunha A. L. M. C., Ziolli R. L., Aucelio R. Q.

Metrology and Measurement Systems

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2007

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Vol. 14, nr 1

125-135

EN

A factorial design was applied for the development of a solid surface room-temperature phosphorimetric method aiming the selective determination of chrysene. Data analysis was made using statistical experimental analysis (testing the significance of the factors using the analysis of variation, F-test and t-test), graphic method (Pareto´s chart) and the evaluation of the interactions among all variables. This procedure was used in order to guarantee high accuracy of results and minimization of the time spent for optimization. As the result, the experimental conditions using a selective phosphorescence inducer (silver) and a substrate surface modifier allowed the determination of chrysene in the presence of pyrene. The method allowed the detection of effective masses of chrysene in the ng range. Method validation is presented including a recovery and "t" tests using a Standard Reference Material.

6

Reducing yarn hairiness in winding by means of jets: optimisation of jet parameters, yarn linear density and winding speed

Rengasamy R. S., Kothari V. K., Patnaik A., Ghosh A., Punekar H.

Autex Research Journal

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2005

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Vol. 5, no. 3

127--132

EN

Reducing yarn hairiness during yarn winding by the use of air jets is a new approach, since the production rate of winding is very high and the process itself increases yarn hairiness. The Box & Behnken factorial design approach has been used to optimise the jet angle, the jet diameter, yarn linear density and the winding speed in order to reduce the yarn hairiness. A jet angle of 450, a jet diameter of 2.2 mm, 10 tex yarn and a winding speed of 800 m/min give the optimal results in terms of reducing the hairiness. A CFD (computational fluid dynamics) model has been developed to simulate the airflow pattern inside the jets with the use of Fluent 6.1 software. The air velocity around the core of the jet is the influencing factor in wrapping the hairs on the yarn body.

7

Techniki eksperymentalne w optymalizacji procesu wtryskiwania tworzyw termoplastycznych - skurcz wtórny wyprasek

Bogucki M., Płaska S., Stączek P.

Polimery

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2003

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T. 48, nr 10

714-719

PL

Przedstawiono doświadczalne ujęcie problemu optymalizacji procesu wtryskiwania tworzyw termoplastycznych (polietylenu małej gęstości), stosując wtryskarki ślimakowe o jednym stopniu docisku i stałej prędkości wtryskiwania. W badaniach wykorzystano programy statystyczne dwuwartościowe--frakcyjne oraz metodę największego spadku łącznie stanowiące sekwencyjną procedurę badań doświadczalnych. Rozwiązanie uwzględnia pięć czynników badanych (temperatura formy, temperatura tworzywa, czas wtryskiwania, czas chłodzenia wyprasek, ciśnienie docisku) oraz jeden czynnik wynikowy - skurcz wtórny wyprasek (s). Opisano poszczególne etapy badań optymalizacyjnych, mianowicie badania przeglądowe, poszukiwanie otoczenia ekstremum oraz wyznaczanie modelu aproksymującego wartość s w otoczeniu ekstremum. Określono współrzędne punktu przestrzeni czynnikowej, w przypadku którego s przybiera wartość minimalną. Stwierdzono, że największy wpływ na zmniejszenie skurczu wywiera niska temperatura formy, długi czas chłodzenia wyprasek oraz duża wartość ciśnienia docisku. Omówiona metoda pozwala na uniezależnienie optymalizacji od cech konstrukcyjnych wtryskarki oraz od charakteru i liczby kryteriów optymalizacji.

EN

Experimental presentation of the problem of injection molding of thermoplastics (low density PE) optimization, using injection molding machines of one pressure degree and constant injection rate. The two-level fractional factorial design and the method of steepest descent, being together a sequence procedure of experimental investigations, were used. The solution takes into consideration five investigated parameters (mold temperature, temperature of a polymer, injection time, time of moldings cooling, pressure Table 1) and one result parameter - after-shrinkage of moldings (s). Particular steps of optimization investigations were described, viz. survey measurements (Figs. 1 and 2), looking for extremum neighborhood (Tables 2-5) and determination of a model approximating s value at extremum neighborhood (Table 6, Fig. 4). Coordinates of the point of factorial space for minimal s value were determined (Table 7). It has been found that low temperature of injection mold, long time of moldings cooling and high value of pressure show the biggest effects on shrinkage decrease. The method described let make the optimization independent on injection molding machine construction as well as on character and number of optimization criteria.