The adsorption of metals by clay minerals is a complex process involving different mechanisms, and is controlled by different variables which can interact. The aim of this work was to study the retention mechanisms of Cd on illite. We obtained Cd adsorption isotherms at constant pH, adsorption edges as a function of pH, adsorption isotherms at 5, 25 and 45°C (pH = 7), and response surfaces of the simultaneous effect of pH, initial concentration, ionic strength, and temperature on the retention of Cd on illite. Below pH 6, adsorption of Cd on illite is via ion exchange with H3O+ and Na+ ions which saturate the exchange sites, the exchange with Na+ being the main mechanism between pH 4.5 and 6.0. For pH values >6, the effect of ionic strength on the amount of Cd2+ retained decreased with pH, being negligible at pH 8; the proton stoichiometry was greater than for pH values <6 and an increase in the temperature favored the retention of Cd. These facts are compatible with a more specific process involving hydrolyzed species, in which Cd can associate with illite as an inner sphere complex.

Kaolin waste dumps contain a huge volume of material that cannot be commercialized due to the presence of variable amounts of iron minerals, which impart a yellowish color to the kaolin. Elimination of iron from kaolin using either a chemical or a biological method was the aim of this study. The chemical leaching of iron from kaolin was carried out using response surface methodology to optimize the reaction conditions. Time was found to be the most influential variable, although oxalic acid must be present to leach 32% of the iron. Biological leaching was also assayed for 14 days using a Bacillus strain. The results of bacterial leaching of iron from kaolin showed <1% iron elimination.

As advances in technology have led to increased use of bentonites, more high-quality bentonite has been sought. The volume of high-quality bentonites available is shrinking and use of bentonite reserves containing impurities is inevitable. The aim of this study was to apply Box–Behnken experimental design and response surface methodology to model and optimize some operational parameters of a hydrocyclone to produce three groups of bentonite concentrates. The four significant operational parameters of hydrocyclones are feed solid ratio, inlet pressure, vortex diameter, and apex diameter, and these parameters were varied and the results evaluated using the Box–Behnken factorial design. In order to produce bentonite concentrates using a hydrocyclone, mathematical model equations were derived by computer simulation programming applying a least-squares method, using Minitab 15. Second-order response functions were produced for the swelling and to establish the quantity of smectite in the bentonite concentrates. Predicted values were found to be in good agreement with the experimental values (R2 values of between 0.829 and 0.999 for smectite and three different swelling groups for the bentonites). Although in natural states these bentonites are not suitable for industrial use, enhancements were obtained giving up to 81.45% smectite and by increasing swelling by 194% for the three bentonite groups. The swelling properties of the bentonites are improved by increasing the proportion of smectite content. The graphics were designed to relate swelling and smectite content according to the two-dimensional hydrocyclone factors, and each factor was evaluated in itself. The present study revealed that the Box–Behnken and response surface methodology can be applied efficiently to model the hydrocyclone for bentonite; the method is economical and provides the maximum amount of information in a short period of time and with the smallest numberof experiments.

At present, no production of zeolites is ongoing in Colombia; thus, because of the high demand in the industrial sector, ~2500 tons is imported annually from other countries such as Cuba, Ecuador, Mexico, and the United States. In order minimize the need for these costly imports, the present study sought to evaluate the viability of producing low-silica zeolites through the hydrothermal synthesis of a Colombian kaolin, which contains quartz (40%) and iron-oxide impurities. The kaolin was subjected to a milling process to reduce the particle size to the order of 11 μm, and was heat treated to transform it to metakaolin. Optimization of the synthesis variables (Na2O/SiO2 and H2O/Al2O3 ratios, time, and temperature) was accomplished by applying an experimental design based on the ‘Response Surface Methodology’ technique. The degree of crystallinity and the cation exchange capacity (CEC) were used as response variables. The CEC was determined from the NTC 5167 standard. In addition, the mineralogical composition and the zeolite microstructure were evaluated using techniques such as scanning electron microscopy, X-ray diffraction, and solid state nuclear magnetic resonance spectroscopy. The results indicated that synthetic type A zeolites with a CEC value of 442 cmol(+)/kg can be obtained from the Colombian kaolin, with the following optimal processing conditions: Na2O/SiO2 molar ratio of 2.7, H2O/Al2O3 molar ratio of 150, temperature = 66°C, and processing time = 8 h. Note that this value (442 cmol(+)/kg) is greater than that reported for an imported commercial zeolite (408 cmol(+)/kg) of the same type, which is currently being used in industry in Colombia. The nationwide availability of the raw material and the quality of the final product present opportunities to make this material available to the Colombian market.

The surface modification of Zeolite 4A using cetyl trimethyl ammonium bromide (CTAB) as a modifier via an ultrasonic method was carried out and the surface physicochemical properties measured. Response surface methodology (RSM) was developed with CTAB concentration, handling time, and handling temperature as variables, to help predict the performance of the modified zeolite under particular conditions. The influence of organic-modified surface treatment and of the amount of modified zeolite on the water-absorption capability of starch-g-poly (acrylic acid) hydrogel composites was also assessed. The results showed that the channels and skeleton structure of zeolite 4A were unchanged after organic modification by CTAB and the surface modification was effective. The results suggest that organic-modified zeolite 4A has improved the water-absorption capability.

In this study a robust design method is developed for extracting Li from boron (B) clays with the aim of minimizing cost and maximizing productivity. Lithium is commercially extracted from brines and certain minerals. Its extraction from clays has previously been found to be expensive, a major part of the extraction cost being attributed to the raw materials used. In this study, raw materials from lower-cost resources are used without applying any standardization to them and this might increase variation in the results. To minimize the variation, and achieve high extraction levels, robust design, statistical design and analysis of experiments, and response surface methodologies are utilized. As a result, consistently higher extraction levels have been achieved compared to previous studies. The experiments were conducted using the Bigadiç boron clay fields in Turkey. However, the method is generally applicable to other cases also.

Eggnog, a dairy-based beverage, comprises both milk and egg proteins. We aimed at optimizing the eggnog formulation using Box–Behnken design of response surface methodology. The combined effects of milk (60–75), cream (25–35) and eggnog base (6–8, all three as g 100/ml) were investigated on heat coagulation time, viscosity and thermal gelation temperature. ANOVA indicated that experimental data were well explained by a quadratic model with high check values (R2 > 0.94) and non-significant lack of fit tests. Based on the responses, an optimized formulation of eggnog with 60.0 milk, 25.0 cream and 6.50 eggnog base (as g 100/ml), could be considered best for manufacturing eggnog with desired attributes. This optimized formulation was characterized for physico-chemical, microbial and sensory attributes and the results indicated significantly higher fat and protein content than control formulation, but lesser lactose and total sugar content. Significantly higher viscosity, heat stability and lower thermal gelation temperature were also observed for the optimized formulation. Coliform, yeast and mold, E. coli and Salmonella counts were not detected in any sample but a significantly lower total plate count was observed for the optimized formulation.

Hierarchical layered double hydroxide (HLDH) was synthesized by using sodium dodecyl sulfate (SDS) as a soft-template agent for the removal of two charged organic dyes (i.e. methylene blue (MB; cationic dye) and methyl orange (MO; anionic dye)). The experimental results based on response surface methodology (RSM) demonstrated distinct removal behaviours of HLDH towards these two dyes: (1) the maximum capacity was 416.7 mg g–1 for MO and 58.7 mg g–1 for MB at 25°C; (2) the increase in temperature could enhance MO removal significantly, whereas it had a negligible effect on the MB treatment process; and (3) rapid removal of MB (5 min) compared to MO (480 min) was observed. In addition, the removal process for both dyes was pH-independent. Multiple characterization techniques further revealed the removal mechanisms, demonstrating that SDS played a significant role in the removal of both dyes; that is, MO replaced SDS to be intercalated into the HLDH interlayer via anion exchange. MB could influence the –SO3 group of SDS, resulting in it modifying the electrodensity of SDS. It could then be further combined with an SDS anion (DS–) via hydrophobic and electrostatic interactions to form DS-MB monolayers. This work not only provides an efficient capture agent for charged dyes, but also offers a deep insight into the underlying removal mechanism.

Two novel adsorbents – montmorillonite (Mnt)-hyamine and Mnt-hyamine-sodium dodecyl sulfate (SDS) – were synthesized using Mnt nanoparticles. The modified Mnt and Mnt nanoparticles were used for the removal of crystal violet from water, and they were characterized using various techniques. The effects of pH, time, temperature, adsorbent dosage and initial dye concentration on the dye-removal efficiency were investigated using response surface methodology. The optimum conditions for maximum dye removal were obtained. The optimum conditions for crystal violet adsorption on Mnt-hyamine, Mnt-hyamine-SDS and Mnt nanoparticles are temperatures 25.00°C, 29.97°C and 27.28°C; pH values 9.00, 10.41 and 9.40; adsorbent dosages 1.00, 1.15 and 1.06 g L–1; and initial dye concentrations 30.00, 98.74 and 99.44 mg L–1, respectively. The adsorbent dosage is the most critical variable for dye removal. Temkin and Langmuir are the best isotherms for studying adsorption equilibria. In the kinetic study, the fractal-like integrated kinetic Langmuir model was the most appropriate model, and the thermodynamic parameters were also determined. The synthesized adsorbents could be easily separated from solution. The Mnt-hyamine-SDS adsorbent has a high adsorption capacity (690.69 mg g–1) for the removal of crystal violet.

In this Research Communication we describe the optimisation of spray drying conditions in the production of microencapsulated cream powder. Oil-in-water emulsions were prepared using maltodextrin (18 DE) and sodium caseinate as wall materials (with the total wall material per total solid content ratio of 30%) and then converted into powder by spray drying. Response surface methodology was used to optimise the factors of spray drying system i.e. inlet drying temperature, feed flow rate, and aspiration rate, where the levels were in the range of 150–190°C, 9–30 ml/min, and 50–100%, respectively. Our objective was to perform spray drying with the highest drying yield and to obtain a microencapsulated cream powder with the highest bulk density, the shortest wetting time, and the lowest surface fat content. The calculated and validated optimum conditions for the spray drying process were found to be 162.8°C for inlet drying temperature, 11.51 ml/min for feed flow rate, and 72.8% for aspiration rate. At these optimum conditions, drying yield, bulk density, wettability, and surface fat content values were 36.37%, 269.9 kg/m3, 115.2 s and 26.2%, respectively.

This study focused on the ability of the Antarctic bacterium Rhodococcus sp. strain AQ5-14 to survive exposure to and to degrade high concentrations of phenol at 0.5 g l-1. After initial evaluation of phenol-degrading performance, the effects of salinity, pH and temperature on the rate of phenol degradation were examined. The optimum conditions for phenol degradation were pH 7 and 0.4 g l-1 NaCl at a temperature of 25°C (83.90%). An analysis using response surface methodology (RSM) and the Plackett-Burman design identified salinity, pH and temperature as three statistically significant factors influencing phenol degradation. The maximum bacterial growth was observed (optical density at 600 nm = 0.455), with medium conditions of pH 6.5, 22.5°C and 0.47 g l-1 NaCl in the central composite design of the RSM experiments enhancing phenol degradation to 99.10%. A central composite design was then used to examine the interactions among these three variables and to determine their optimal levels. There was excellent agreement (R2 = 0.9785) between experimental and predicted values, with less strong but still good agreement (R2 = 0.8376) between the predicted model values and those obtained experimentally under optimized conditions. Rhodococcus sp. strain AQ5-14 has excellent potential for the bioremediation of phenol.

A zeolite-montmorillonite (zeolite-Mt) nano-adsorbent was prepared by calcination at 600°C. The synthesized nano-adsorbent was tested for removal of a toxic and cationic dye (crystal violet) from water, and it was characterized by various techniques. The effects of variables such as pH, temperature, adsorbent dosage and initial dye concentration on the removal efficiency of the dye were investigated by response surface methodology (RSM). Experimental conditions were optimized by RSM to achieve the maximum dye removal efficiency. Optimum conditions for maximum removal of dye were obtained at pH 9, temperature of 25°C, adsorbent dosage of 2 g L−1 and initial dye concentration of 40 mg L−1. Under these conditions, the maximum removal efficiency obtained was 99.9%. Various isotherms were applied to study adsorption equilibrium, and of these, the Freundlich isotherm provided the best fit. In addition, the fractal-like integrated kinetic Langmuir model was the most appropriate among several kinetic models. The thermodynamic parameters were also determined. The zeolite-Mt prepared under optimum conditions displayed a greater adsorption capacity than activated carbon (manufactured by Merck) and than various other adsorbents.

The application of natural fertilizer mixtures that improve nutrient retention ability of soils has attracted considerable attention in recent years. In addition to rock phosphate (RP), the basic components of these mixtures are zeolites modified with selected cations, such as the ammonium ion. The NH4-zeolite serves as a carrier of nutrients as well as a soil conditioner, and it promotes the RP dissolution in all soil types. The purpose of the present work was to prepare costeffective NH4-zeolite supplement, using 32 full factorial experimental designs, with concentration of modifier and processing time as variables. Saturation processes were carried out on two types of natural zeolites, K- clinoptilolite (K-Cp) and Ca-clinoptilolite (Ca-Cp). The Response Surface Method (RSM) was applied for evaluation of cation exchange, suggesting an effective NH4+ modification of natural zeolite at lower quantities of modifier than commonly found in other studies on the topic. Using Principal Component Analysis (PCA), differences between samples relative to the process variables were clearly outlined and correlated with concentrations of the exchanged cations. The best results were obtained for the K-Cp type modified with 1.5 M solution of ammonium sulfate (at a Cp/NH4+ stochiometric ratio 1:7.5) for all three processing intervals. By optimizing the modification process parameters, an experimental design of partially saturated NH4-Cp supplement that has the potential to supply all major plant nutrients was proposed.

The experiments reported in this research paper describe the effects of β-galactosidase enzyme dose and cheese whey amount, on the maximum concentration and yield of galacto-oligosaccahride (GOS) and reaction time. The experimental plan was based on central composite rotational design (CCRD) and modelled by response surface methodology (RSM). The results indicate that the proposed mathematical models could adequately describe the concentration and yield of GOS and the reaction time within the limits of the factors that are being investigated. The variance analysis shows high values of coefficients of determination (>0·97) while no significant lack of fit was evident. Hence, the models could be employed to select reaction conditions applied in the manufacture of products enriched in bioactive compounds with high value-added.

The recovery of milk constituents from cheese whey is affected by various processing conditions followed during production of Ricotta cheese. The objective of the present investigation was to optimize the temperature (60–90 °C), pH (3–7) and CaCl2 concentration (2·0–6·0 mm) for maximum yield/recovery of milk constituents. The research work was carried out in two phases. In 1st phase, the influence of these processing conditions was evaluated through 20 experiments formulated by central composite design (CCD) keeping the yield as response factor. The results obtained from these experiments were used to optimize processing conditions for maximum yield using response surface methodology (RSM). The three best combinations of processing conditions (90 °C, pH 7, CaCl2 6 mm), (100 °C, pH 5, CaCl2 4 mm) and (75 °C, pH 8·4, CaCl2 4 mm) were exploited in the next phase for Ricotta cheese production from a mixture of Buffalo cheese whey and skim milk (9 : 1) to determine the influence of optimized conditions on the cheese composition. Ricotta cheeses were analyzed for various physicochemical (moisture, fat, protein, lactose, total solids, pH and acidity indicated) parameters during storage of 60 d at 4 ± 2 °C after every 15 d interval. Ricotta cheese prepared at 90 °C, pH 7 and CaCl2 6 mm exhibited the highest cheese yield, proteins and total solids, while high fat content was recorded for cheese processed at 100 °C, pH 5 and 4 mm CaCl2 concentration. A significant storage-related increase in acidity and NPN was recorded for all cheese samples.

The first three essential amino acids (EAA) for broilers including methionine (Met), lysine (Lys) and threonine (Thr) may greatly influence the growth of chick muscles at early stages of life. In order to survey the potential effects of those EAA on growth muscles, a rotatable three-variable central composite design (CCD) was conducted to track the interrelationships of dietary digestible Met (dMet), Lys (dLys) and Thr (dThr) for optimization of processing yields in broiler chicks using response surface methodology. A total of 60 floor pens of six birds each were assigned to 15 dietary treatments based on CCD containing five levels of dMet (0.416% to 0.584% of diet), dLys (0.881% to 1.319% of diet) and dThr (0.532% to 0.868% of diet) from 3 to 16 days of age. Experimental treatments significantly affected breast mass (BM) and leg mass (LM) of the birds (P<0.05) in which the main effect of dLys on BM was threefold higher than the main effect of dThr, and interaction effect between dMet and dLys was observed on BM (P<0.05). However, in the case of LM, the main effect of dThr was higher than the main effects of dMet and dLys and highest interaction effect exist between dThr and dMet (P<0.05). The second-order models for BM and LM were fitted by least squares regression. Canonical analysis revealed that the stationary points for carcass components were saddle points, thus ridge analysis was performed for getting optimal values of each EAA. Ridge analyses of BM and LM models showed that the maximum BM point may be obtained with 0.58%, 1.05% and 0.76% of dMet, dLys and dThr, respectively, in diet, and maximum LM point may be achieved with 0.58%, 1.09% and 0.70% of dMet, dLys and dThr, respectively, in diet. The resultant ideal ratios of dMet and dThr to dLys were 55% and 72% for BM; 53% and 64% for LM. Moreover, sensitivity analysis showed that the most important amino acids in BM and LM models were Lys and Thr, respectively. In conclusion, providing these three amino acid for BM optimization may warrant LM optimization and higher ideal ratios of dMet and dThr for breast muscle may indicate the higher importance of these EAA in this muscle than those in thigh muscle.

Plasma etching process plays a critical role in semiconductor manufacturing. Becausephysical and chemical mechanisms involved in plasma etching are extremely complicated,models supporting process control are difficult to construct. This paper uses a 35-runD-optimal design to efficiently collect data under well planned conditions for importantcontrollable variables such as power, pressure, electrode gap and gas flows ofCl2 and He andthe response, etching rate, for building an empirical underlying model. Since therelationship between the control and response variables could be highly nonlinear, ageneralized regression neural network is used to select important model variables andtheir combination effects and to fit the model. Compared with the response surfacemethodology, the proposed method has better prediction performance in training and testingsamples. A success application of the model to control the plasma etching processdemonstrates the effectiveness of the methods.

This study was aimed to optimise lactose, inulin and yeast extract concentration and also culture pH for maximising the growth of a probiotic bacterium, Bifidobacterium animalis subsp. lactis in apple juice and to assess the effects of these factors by using response surface methodology. A second-order central composite design was applied to evaluate the effects of these independent variables on growth of the microorganism. A polynomial regression model with cubic and quadratic terms was used for analysis of the experimental data. It was found that the effects involving inulin, yeast extract and pH on growth of the bacterium were significant, and the strongest effect was given by the yeast extract concentration. Estimated optimum conditions of the factors on the bacterial growth are as follows: lactose concentration=9·5 g/l; inulin concentration=38·5 mg/l; yeast extract concentration=9·6 g/l and initial pH=6·2.

Goat milk protein was hydrolysed with subtilisin and trypsin. As input variables, temperature was assayed in the interval 45–70 °C for subtilisin and 30–55 °C for trypsin, while the enzyme-substrate ratio varied from 1 to 5%. The effect of the input variables on the degree of hydrolysis and ACE-inhibitory activity (output variables) was modelled by second order polynomials, which were able to fit the experimental data with deviations below 10%. The individual maximum values of the degree of hydrolysis and the ACE-inhibitory activity were found at conflicting conditions of temperature and enzyme-substrate ratio. Since such maximum values could not be reached simultaneously, a bi-objective optimisation procedure was undertaken, producing a set of non-inferior solutions that weighted both objectives.

The goal of this study is to empirically investigate the major hot rolling processparameters affecting the yield strength, ultimate tensile strength and strain-hardeningexponent of Nb-microalloyed steel sheets. The parameters considered were the roughing,finishing and coiling temperatures. Three levels for each parameter were used to develop amodel relating the process parameters to mechanical properties. By applying the responsesurface methodology, analysis of variance was done to determine the mathematical modelsrelated to each response. The results indicated that decreasing the coiling and finishingtemperatures significantly influenced the mechanical properties. Also, the modelspredicted that the maximum yield strength, ultimate tensile strength and strain-hardeningexponent are simultaneously obtained under the following conditions: roughing temperature= 1097 °C, finishing temperature = 837 °C and coiling temperature = 580 °C. The predictedvalues were close to the experimental values, indicating the suitability of themodels.