Range Of Initial Concentrations Research Articles

Efficient removal of methylene blue using Algerian purified bentonite/sodium alginate beads in batch, recirculating, and continuous adsorption processes

ABSTRACT In this study, an encapsulated purified bentonite/sodium alginate composite (PB/SA) was successfully prepared by solution intercalation and ionic crosslinking using calcium chloride. The PB/SA adsorbent was characterised by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer–Emmett–Teller method (BET) from N2 adsorption-desorption isotherm at 77 K, thermogravimetric analysis (TGA), and the point of zero charge (pHPZC). Adsorption efficiency of PB/SA was studied by using methylene blue dye (MB) in batch, recirculating and continuous systems. The effect of certain parameters on the adsorption capacity in the different systems was investigated. The results from batch study showed that MB removal increased with increasing adsorbent dose and pH solution. The test of operating parameters in continuous system, such as the bed height and the adsorbate flow rate, showed that MB removal increases at lower flow rate (2 mL/min) and higher bed height (2.4 cm). Kinetics modelling shows that the adsorption of MB onto PB/SA in batch and recirculating processes was well described by the pseudo-first-order model with high coefficient correlation R2 (0.99). Regarding results from isotherms, the MB adsorption follows the Langmuir isotherm with R2 exceeding 0.99 justifying monolayer and homogeneous adsorption. In addition, when comparing batch and recirculating processes, we observed that for a range of initial concentrations from 10 to 100 mg/L, the maximum adsorbed amounts were found to be 100 mg/g and 86.6 mg/g respectively for batch and recirculating systems. However, these values are higher in isotherms modelling because the results were fitted and compared only for low concentrations without the equilibrium lines. Hence, PB/SA beads can be a promising material for enhancing the elimination of dyes from an aqueous solution in different adsorption processes.

Degradation of phenanthrene by consortium 5H under hypersaline conditions

PAHs have been widely detected to accumulate in saline and hypersaline environments. Moderately halophilic microbes are considered the most suitable player for the elimination of PAHs in such environments. In this study, consortium 5H was enriched under 5% salinity and completely degraded phenanthrene in 5 days. By high-throughput sequencing, consortium 5H was identified as being mainly composed of Methylophaga, Marinobacter and Thalassospira. Combined with the investigation of intermediates and enzymatic activities, the degradation pathway of consortium 5H on phenanthrene was proposed. Consortium 5H was identified as having the ability to tolerate a wide range of salinities (1%–10%) and initial PAH concentrations (50 mg/L to 400 mg/L). It was also able to function under neutral to weak alkaline conditions (pH from 6 to 9) and the phytotoxicity of the produced intermediates showed no significant difference with distilled water. Furthermore, the metagenome of consortium 5H was measured and analyzed, which showed a great abundance of catabolic genes contained in consortium 5H. This study expanded the knowledge of PAH-degradation under hypersaline environments and consortium 5H was proposed to have good potential for the elimination of PAH pollution in saline/hypersaline environments.

Highly recyclable surfactant-based supramolecular eutectogels for iodine removal

In this work, we screened several surfactants for their ability to harden Eutectic Mixtures. We found cetyldiethanolamine-N-oxide as the best candidate, which was able to form eutectogel in four eutectic mixtures. Characterization of the gels obtained in terms of thermal stability, rheology and gelation kinetics, showed a prominent influence of the nature of the hydrogen bonding accepting and donating components for the first two parameter and the other one, respectively. Then, we assessed the eutectogels for their ability to adsorb I2, as a model for its radioactive nuclides, from apolar solvent solutions. The best performing gel allowed fast and thorough removal of I2, over a broad range of initial concentrations. This gel displayed a maximum adsorption capacity of 280 mg/g, competitive with most gel-based sorbent reported in the literature for the adsorption of iodine. Interestingly, the eutectogel proved to be highly recyclable, it could be regenerated and reused without loss in performance.

Synthetic azo dye bio-decolorization by Priestia sp. RA1: process optimization and phytotoxicity assessment.

Azo compounds represent the most diverse group of colorants widely employed in industrial sectors. Being highly toxic and recalcitrant compound, azo dyes pose a threat to plants, animals, and humans. In the present report, bio-decolorization of azo dye, reactive black 5, was evaluated by newly isolated Priestia sp. RA1. Strain RA1 was able to decolorize 97% of 100ppm reactive black 5 in 60h. Specific activity of dye decolorization was found to be 0.233μmolmin-1g-1 dry cells. Successful decolorization over a broad range of pH, salinity, temperature, and initial dye concentration was observed. Phytotoxicity assay on agriculturally important crops showed considerable difference in percentage seed germination and growth when treated with original and bio-decolorized dye samples. Bio-decolorization at high dye concentrations, promising decolorization rate, and non-toxic nature of treated products suggest the potential of strain RA1 for bioremediation of dye-contaminated water and its re-use in the industries.

Reactive liquid–liquid extraction of bio-based 3-hydroxypropionic acid using a biocompatible organic phase containing a tertiary amine: A model-based approach to elucidate dominant mechanisms

This work studies reactive liquid–liquid extraction of 3-hydroxypropionic acid (3-HP) from aqueous solutions using a biocompatible organic phase consisting in N,N-didodecylmethylamine (DDMA) (20% v/v) diluted in 1-dodecanol (40% v/v) and dodecane (40% v/v). The objective was to propose an equilibrium model based on the law of mass action accounting for the main phenomena occurring in the system. A set of equilibrium extraction experiments was performed in the initial acid concentration range 0.0028 – 1 mol L-1 in order to determine the extraction yield, equilibrium pH and to collect infrared spectra of the loaded organic phases. FT-IR spectra allowed to identify and elucidate the main mechanisms of acid–amine interaction, which were taken into account in the model. The formation of 1:1 acid–amine stoichiometry complex through ion-pairing was determined as the dominant mechanism in all the concentration range. For initial acid concentrations above 0.11 mol L-1, the formation of 2:1 acid–amine complexes through H-bonding of acid molecules with 1:1 complexes was also observed and determined to be almost as important as ion-pair formation at 1 mol L-1. The presence of impurities in the organic phase was taken into account by introducing a side reaction essential to represent low extraction yields and high equilibrium pH values observed at low initial acid concentrations (< 0.02 mol L−1). A global sensitivity analysis of the model’s parameters pointed out three concentration regions based on the relative contribution of each phenomenon: (i) for initial acid concentrations below 0.02 mol L−1, the main phenomena are 1:1 ion-pair formation and the side reaction; (ii) between 0.02 mol L−1 and 0.11 mol L−1, mainly 1:1 ion-pair formation; and (iii), for concentrations above 0.11 mol L−1 both considered complexation reactions i.e., 1:1 ion-pair formation and 2:1 H-bonding. The proposed model allowed thus to evaluate the relative importance of the phenomena occurring in the system in all the studied acid concentration range.

Co-doped Fe-MIL-100 as an adsorbent for tetracycline removal from aqueous solution.

In the study, Fe-MIL-100 was modified by adding Co2+ in the synthesis process; Co/Fe-MIL-100 was successfully synthesized and used to adsorb tetracycline. The addition of Co2+ increased the thermal stability of Fe-MIL-100 without changing the crystal structure. It was found that Co/Fe-MIL-100 exhibited satisfactory performance in tetracycline removal, the tetracycline removal efficiency reached almost 100% in the initial concentration range of 10-40mg/L, and it still reached 82.38% under the condition of 60mg/L tetracycline. Besides, the factors of tetracycline concentration, pH and inorganic anion on removal efficiency were explored. The coexistence of inorganic anion decreased the adsorption capacity of tetracycline due to the competitive adsorption. CO32- had a more obvious inhibition effect on the adsorption efficiency of tetracycline than Cl-. The fitting correlation coefficient of Langmuir model was higher and the kinetics better fitted by pseudo-second-order, respectively. As a result of its high removal efficiency and excellent recycling performance, it has great potential in application fields such as removing tetracycline from wastewater.

Complete genome sequences of the antibiotic sulfamethoxazole-mineralizing bacteria Paenarthrobacter sp. P27 and Norcardiodes sp. N27.

Sulfonamide antibiotics (SAs) have been produced and consumed on a large scale over the last few decades. SAs are a typical class of refractory contaminants that are omnipresent in various environments. Although several [phenyl]-SA-degrading bacteria and their corresponding genomes have been documented, limited genetic information is available for the degraders of heterocyclic products (e.g., 3-amino-5-methylisoxazole [3A5MI] produced via sulfamethoxazole [SMX] catabolism). In this study, the previously isolated SMX-mineralizing bacterial partners, Paenarthrobacter sp. P27 (responsible for the initial cleavage of the -C-S-N- bond of SMX and further degradation of [phenyl]-SMX) and Norcardiodes sp. N27 (responsible for 3A5MI catabolism), were further studied and their complete genomes were sequenced. Complete degradation and bacterial growth were verified by pure-culture experiments with SMX or 3A5MI as the sole carbon, nitrogen, and energy source. By cross-feeding strains P27 and N27, complete catabolism of SMX could be achieved over a wide range of initial SMX concentrations. Moreover, strain P27 was capable of transforming the additional nine SA representatives into their corresponding nitrogen-containing heterocyclic products, strongly indicating the broad substrate spectrum and marked bioremediation potential of strain P27. The genome of strain P27 contained the highly homologous monooxygenase gene cluster, sadABC, which initially attacked the sulfonamide molecules. The complete genome sequences of the two important degraders will benefit future research centering on the molecular mechanism underlying advanced SMX mineralization and will aid in further understanding the interspecific interactions and metabolite exchanges for the optimization of artificially constructed synthetic functional microbiomes.

Fabricating amide functional group modified hyper-cross-linked adsorption resin with enhanced adsorption and recognition performance for 5-hydroxymethylfurfural adsorption via simple one-step

In this study, three kinds of amide functional group modified hyper-cross-linked adsorption resin were synthesized by alternating radical copolymerization in simple one-step and applied for 5-hydroxymethylfurfural (5-HMF) adsorption. The successful synthesis and properties of adsorbents were evaluated with Fourier transform infrared spectroscopy, scanning electron microscopy, nitrogen adsorption–desorption isotherms, thermogravimetric analysis, and elemental analysis. Poly ( N , N ′-4,4′-diphenylmethane-bismaleimide-alt-divinylbenzene) (poly (BDM-alt-DVB)) resin exhibited highest adsorption capacity for 5-HMF (64.0 mg·g −1 wet resin) and excellent adsorption selectivity ( α 5-HMF/LA = 2.71 ± 0.12, α 5-HMF/FA = 13.88 ± 0.15, α 5-HMF/Glucose = 11.91 ± 1.11) in the multi-component solution at 25 °C. Langmuir isotherm model well fitted the equilibrium adsorption data within the initial 5-HMF concentration range of 0.5–10.0 g·L −1 with highest correlation coefficient. Furthermore, the thermodynamic parameters demonstrated that the adsorption of 5-HMF onto poly (BDM-alt-DVB) resin was spontaneous and exothermic. Kinetic study revealed that the adsorption process was fast, reaching equilibrium within 12 min. Importantly, the poly (BDM-alt-DVB) resin also demonstrated excellent reusability. In summary, the poly (BDM-alt-DVB) resin will be useful in 5-HMF hydrolysate separation applications.

Calcium carbonate as sorbent for lead removal from wastewaters

Low-cost and largely available industrial by-products such as calcite (CaCO3) have been considered as sorbents to remediate wastewaters from toxic elements, such as lead, in compliance with the European circular economy strategy. To date few articles are reporting results on lead sorption at the calcite-water solution interface by X-ray photoelectron spectroscopy (XPS) and this investigation aims to clarifying the mechanism of the interaction of Pb2+ model solutions over a wide concentration range, from 0.1 μM to 80 mM, with commercial calcite.X-ray powder diffraction (XRPD), scanning electron microscopy (SEM, EDX) and XPS analysis indicate that when CaCO3 particles are soaked in Pb2+ 0.1 mM and 1 mM solutions, hexagonal platelets of hydrocerussite [(PbCO3)2 Pb(OH)2] precipitate on its surface. When the concentration of Pb2+ is equal or higher than 40 mM, prismatic acicula of cerussite [PbCO3] precipitate. Solution analysis by atomic emission spectroscopy (ICP-AES) and ICP-mass spectrometry (ICP-MS) indicate that Pb2+ removal efficiency is nearly 100%; when the initial Pb2+ concentration was equal to 0.1 μM it was below the limit of detection (LOD) and the efficiency could not be determined. The sorption capacity (qe) increases linearly with increasing initial Pb2+ concentration up to a value of 1680 (20) mg/g when the initial Pb2+concentration is 80 mM.These findings suggest that heterogeneous nucleation and surface co-precipitation occur and calcite can be well considered a very promising sorbent for Pb2+ removal from wastewaters within a wide initial concentration range.

Monte Carlo simulation of solution polymerization of butyl acrylate over a wide range of temperatures

Simulation of solution polymerization of butyl acrylate, in an acceptable agreement with experimental data, over a wide range of temperatures is still challenging due to the inaccuracy of the rate coefficients of the competing reactions. Therefore, in this study, a massive set of simulations was performed to determine the best set of reaction rate coefficients to predict the process with an excellent agreement with experimental data over a wide range of initiator and monomer concentrations and temperatures. To this end, a randomized factorial design in combination with Monte Carlo simulations and analysis of variance were employed to acquire the best set of reaction rate coefficients. In total, 1692 simulations were performed. Subsequently, the polymerization process was simulated by using the obtained reaction rate coefficients. An excellent agreement between the simulation and experimental data was observed over a wide range of temperatures. The trends of the time course of weight average molecular weight, and the time course of propagation reaction to intramolecular chain transfer reaction were similar. Furthermore, variations of molecular weight, branching level, and macromonomer content with reaction temperature were calculated. The results can be used to obtain well-defined and targeted acrylic microstructures by controlling the reaction conditions.

Evaluating biohydrogen production by Clostridium hydrogenum sp. nov. strain CUEA01 isolated from mangrove sediments in Thailand

The hydrogen (H 2 ) fermentative Clostridium hydrogenum sp. nov. strain CUEA01 was isolated from a mangrove sediment in Thailand. Genome sequencing and analysis revealed a genome size of 5,501,482 bp that encoded for 3,292 predicted protein coding genes with annotated functional assignments and many genes associated with carbon utilization and H 2 evolution. The H 2 production performance was evaluated in batch fermentation, and revealed that this strain can grow and produce H 2 at a broad range of temperatures (15–40 °C), pH (4–10), and initial glucose concentrations (5–60 g/L). The maximum H 2 yield (3.11 mol H2 /mol glucose ) was obtained at 37 °C, pH 8, and an initial glucose concentration of 10 g/L. Furthermore, this strain could utilize various carbon sources, including xylose, xylan, starch, mannose, glycerol, and avicel cellulose, amongst others. Additionally, CUEA01 was compatible with agro-industrial wastes and could achieve a maximum CHP of 4639 mL/L and 4024 mL/L from sugarcane molasses and cassava pulp, respectively. This demonstrates that CUEA01 has a potential for H 2 fermentation from complex organic wastes since it can secrete enzyme cocktails that consolidate the fermentation process. • Discovery and reported characteristic of Clostridium hydrogenum sp. nov CUEA01. • Draft genome sequencing of CUEA01 isolated from mangrove sediments in Thailand. • CUEA01 was compatible with various carbon sources e.g., glycerol, starch, xylose. • CUEA01 produced maximum H 2 yield of 3.11 mol H2 /mol glucose . • CUEA01 produced cumulative H 2 production of 4639 mL/L from agro-industrial wastes.

Enhanced removal of phosphate from wastewater by precipitation coupled with flocculation

Eco-friendly flocculants of alginic acid, NaHCO3 and CaCl2.2H2O with advantages of strong gelation characteristics were prepared for supporting the removal of phosphate in synthetic wastewater using CaO and Ca(OH)2 as precipitants. The effects of weight ratios of each component in flocculants, dosage of flocculants and initial phosphate concentration were investigated through batch of experiments. The results showed excellent flocculation performance with the weight ratio of alginic acid:NaHCO3 and CaCl2.2H2O at 1:0.3:0.02 and the dosage of flocculants at 0.0050 g/25 mL of phosphate solution in the range of initial phosphate concentration from 50 to 1000 ppm. Comparing to the sample without flocculants, the phosphate removal efficiency using CaO and Ca(OH)2 with the addition of flocculants increased from 19 and 20% to 97% at the initial phosphate concentration of 50 ppm, respectively by filtration of filter paper 2.7 μm.

Sustainable Durio zibethinus-Derived Biosorbents for Congo Red Removal from Aqueous Solution: Statistical Optimization, Isotherms and Mechanism Studies

This investigation reports on the biosorption mechanism of Congo Red dyes (CR) in aqueous solution using acid-treated durian peels, prepared for this study. The biosorbent nature was characterized using the Scanning Electron Microscopy (SEM), Fourier Transform infrared spectroscopy (FT-IR) and Brunaure-Emmet-Teller (BET). The effect of process parameters within operational range of pH (2–9), contact time (10–200 min), initial concentration (25–400 mg g−1) and temperature (25–65 °C) for the optimum removal of CR dyes was investigated using central composite design (CCD) under response surface methodology (RSM), and revealed that the optimum condition of biosorption was achieved around a pH of 5.5, contact time of 105 min at initial concentration of 212.5 mg L−1 within 45 °C temperature, which corresponds to 95.2% percent removal of CR. The experimental data fitted better to the second order polynomial model, with a correlation coefficient R2 value of 0.9917 and the Langmuir isotherm model with biosorption capacity of 107.52 mg g−1. Gibbs free energy indicated that the adsorption of CR dyes was spontaneous. The mechanism of the adsorption of CR dyes revealed that the biosorption of CR dyes investigated under different operational conditions show that under acidic pH, the adsorption efficiency of the acid treated durian peels is enhanced for the adsorption of CR dye molecules.

Physical and chemical properties of binary mixtures of dibutylammonium-based ionic liquids and water

Ionic liquids are used in different processes owing to their low vapor pressure, large viscosity range, chemical and thermal stability, and superior conductance even without water. These features make them flexible and tunable, indicating their possible use as substitutes for commonly used compounds in many processes. The objective of this study was to evaluate the properties of aqueous binary solutions for three different ionic liquids (ILs): dibutylammonium acetate, dibutylammonium propanoate, and dibutylammonium butanoate. The measured properties were density, speed of sound, and conductivity, and their isentropic compressibility and thermal expansion coefficient were calculated based on these properties. The temperature range used for measurements was 293.15–323.15 K. Mathematical models were used for each ionic liquid + water mixture to fit the density and speed of sound data. The increase in the alkyl chain leads to a tendency to decrease the values of density, speed of sound, and conductivity of the solutions. However, decreasing the dilution in water, the density, the conductivity and the speed of sound initially increase and then decrease, exhibiting a maximum in the initial water concentration range which indicates the formation of aggregates. Critical micellar concentrations at 298 K were determined through conductivity data. Enhancing the temperature leads to a decrease on density and sound velocity.Supplementary InformationThe online version contains supplementary material available at 10.1007/s43153-021-00174-7.

Design of combustion experiments using differential entropy

The aim of several combustion experiments is the determination of the rate coefficients of important elementary reactions. The experimental conditions are usually selected on the basis of local sensitivity analysis. Shock tube and tubular flow reactor experiments are often designed in such a way that only one reaction step is important at the investigated conditions. Sheen and Manion (J. Phys. Chem. A, 118 (2014) 4929–4941) suggested a method for the design of shock tube experiments based on differential entropy. Their method was modified and extended in this work. In the extended method, both the experimental and residual errors of the measurements are considered at the calculation of the posterior uncertainty of the determined rate parameters, the differential entropy matrix is calculated in an analytical way and the net information flux value is calculated for each suggested experimental point. In an iterative procedure, all investigated experimental points with negative net information flux values are discarded and the remaining experimental conditions are recommended for the measurements. The most valuable candidate experimental points can be determined based on the net information flux values. The method was used for the selection of experimental conditions for the determination of the rate coefficient of reaction NO2 + H = NO + OH at conditions similar to the tubular flow reactor experiments of Alzueta et al. (Energy Fuels, 15 (2001) 724–729). In these experiments, the oxidation of methanol was investigated with and without NO addition. Our method suggested a range of temperature, equivalence ratio and initial NO concentration, where the experimental data carry the most information on the rate coefficient of this elementary reaction.

Conversion of glucose to 5-hydroxymethyl furfural in water-acetonitrile-dimethyl sulfoxide solvent with aluminum on activated carbon and maleic acid

The development of sustainable, efficient routes for conversion of glucose in biomass to 5-hydroxymethylfurfural (HMF), an important green intermediate in the production of value-added chemicals and fuels, has emerged due to the need to replace depletion of non-renewable fossil sources and climate change caused by their use. In this study, we describe a highly efficient reaction system for the production of HMF with a combination of homogeneous catalyst and heterogeneous catalyst in a polar cosolvent. The catalyst system consists of activated carbon (AC) supported aluminum (AC-Al) and maleic acid (MA) dissolved in a mixture of water, acetonitrile (ACN) and dimethyl sulfoxide (DMSO). Kinetic analysis of HMF production from glucose shows that carbon supported aluminum catalyst in combination with homogeneous maleic acid favored fructose dehydration to HMF instead of the formation of insoluble humins when compared to dissolved aluminum chloride and maleic acid in the same solvent. In addition, the rate constant of HMF hydrolysis to levulinic and formic acid was lower for AC-Al compared to dissolved Al. Response surface methodology (RSM), with central composite rotatable design (CCRD), identified the optimum conditions for glucose conversion to HMF as 168 °C for 11 min with a predicted molar yield of 50.3 mol%, which compared well to the experimentally verified yield of 45.8 mol% for these reaction conditions. To test the influence of glucose concentration on HMF yield, a range of initial glucose concentrations were examined. Results showed that the HMF yield increased with the decrease of weight percentage of glucose, suggesting that second order reactions result in humins formation.

Solid-liquid equilibrium of 3,3-dilauryl thiodipropionate/lauryl alcohol in melt crystallization and model based process design

Melt crystallization is a promising and widely used method for obtaining pure compounds. Nonetheless, separation of 3,3-dilauryl thiodipropionate (DLTP) has not yet been realized by melt crystallization. Solid-liquid equilibrium is the fundamental for the separation process design. In this work, we evaluated the feasibility of the purification of DLTP from the DLTP/lauryl alcohol (LA) binary mixture by melt crystallization technique. For this purpose, the solid-liquid equilibrium data were measured using differential scanning calorimetry (DSC) technique. The experimental data were correlated by Wilson, Margules-3-suffix and Non-Random Two-Liquid (NRTL) activity coefficient models to obtain the binary parameters of the three models. Eutectic composition and temperature were calculated using NRTL model, which were xLA = 0.961 (molar fraction) and 295.79 K, respectively. On the basis of the solid–liquid equilibrium, the multistage countercurrent separation configurations were proposed for the separation of the binary system. The formulated Mixed Integer Nonlinear Programming (MINLP) problem was solved using the branch-and-bound algorithm. The conceptual designs for multistage countercurrent configuration were derived based on MINLP optimization by comparing results at various conditions. Results showed that at least 3 crystallization stages with keff ≤ 0.4 are required to obtain the 99% (mass fraction) DLTP product within the initial concentration range from10% to 30% (mass fraction).

Rapid Removal of Methylene Blue in Water Using Polymer-Based Biochar Nanocomposite-Coated Filters

In this study, the effectiveness of novel nanocomposite-coated filters consisting of biochar (BC) functionalized with sodium alginate (SA) and poly (vinyl alcohol) (PVA) was investigated for methylene (MB) blue removal. The filters were fabricated via a dip-coating method and SEM and FTIR spectroscopy confirmed the successful coating of the filters. The impact of the nanocomposite formulation and the operating parameters (initial pH and MB concentration) on the performance of the coated filters were studied. A nanocomposite composition consisting of 1.0 wt.% SA, 2.0 wt.% PVA, and 1000 ppm BC were found to be optimum, reaching as high as 96.51% MB removal. The fabricated filters were determined to be robust over a wide range of pH and initial MB concentrations. The Sips isotherm model proved to be the best-fit model for MB adsorption, where chemisorption dominates at low MB concentrations, while physisorption dominates at high MB concentrations. The filters have a maximum sorption capacity of 54.5198 mg g-1 and showed good reusability. Overall, our synthesized SA/PVA/BC-coated filters can be used to effectively remove dyes in wastewater over a wide range of operating conditions.

The influence of sulfur addition on the hazard-type reaction of ilmenite ores with sulfuric acid

Abstract The paper presents results of thermokinetic investigation of the hazard-type reaction of Norwegian and Australian ilmenite ores with sulfuric acid, modified by the addition of elemental sulfur, to increase the process safety in industrial conditions. In the reactions of both ilmenite ores the addition of sulfur caused a reduction of the thermal power generated in the reaction and a decrease in the value of the thermokinetic parameter ΔTmax/Δτ for almost the whole range of initial concentrations of sulfuric acid. It was also found that the addition of sulfur to the reaction did not negatively affect the degree of ilmenite leaching. The interpretation of the obtained thermokinetic curves allowed to determine safe process conditions for both types of titanium raw materials.

Biochemical inhibition of acid phosphatase activity in two mountain spruce forest soils

The product inhibition of the 4-methylumbelliferyl phosphate (MUB-P) decay rate, a measure of potential acid phosphatase activity, has not been considered in most of the published kinetic studies. The aim of this study was to determine the type and strength of the product inhibition in order to better define reaction conditions at which the acid phosphatase activity assay produces unbiased results. The MUB-P decay rate was measured in the forest floor and topsoil organic horizons of two spruce forest catchments at different initial MUB-P and P-PO43− concentrations. The type and strength of the inhibition was analyzed by non-linear regression. We found that MUB-P decay was competitively inhibited by the P-PO43− but also by dissolved organic P. By using estimated kinetic parameters, we calculated an underestimation of potential acid phosphatase activity by up to ~ 20% at concentrations of added MUB-P as high as 300 µmol g−1 dry weight and an incubation time one hour due to background inorganic and organic P concentrations in range of units of µmol per gram of dry soil. We discuss approaches that can be used to minimize the underestimation and show that the previously defined recommendations might not be always sufficient to avoid the bias. Therefore, we recommend to analyze progress curves at a wide range of initial MUB-P concentrations using non-linear methods when the enzyme assay is optimized for a given soil. When changes in inorganic and/or organic P concentrations are expected, we further recommend measuring background inorganic and organic P concentrations.