Equilibrium Software Research Articles

Leached Copper Correlation with Dissolved Organic Carbon in Sloped Vineyard Soil

The solubility and mobility of copper (Cu) in soil is strongly influenced by the presence of dissolved organic carbon (DOC); however, the interactions between Cu and DOC are complex and not yet fully understood. In this study, Cu and DOC concentrations were measured monthly for two years in leachates from self-constructed lysimeters installed at inter- and intra-row vineyard hilltop, backslope, and footslope areas at the SUPREHILL Critical Zone Observatory, Croatia. The aim was to quantify Cu and DOC leaching from the hilltop towards the backslope and the footslope. The assumed strong relationship between Cu and DOC in the leachates was statistically analyzed and explained using chemical equilibrium software. Leachates were analyzed for pH, EC, DOC, Cu, and major ion concentrations. The highest Cu concentrations found in leachates from the intra-row footslope suggested Cu downhill transport. Although not strong, a significant positive correlation between Cu and DOC in footslope leachates confirmed the relevance of Cu complexation by DOC. Speciation confirmed that more than 99.9% of total Cu in leachates was found as a Cu-DOC complex. Data implied the role of soil water flow pathways in explaining Cu downhill transport. Critical timing for applying Cu fungicides at sloped vineyards was highlighted.

Effect of phosphorus on the toxicity of zinc to the microalga Raphidocelis subcapitata.

The aim of this study was to evaluate the effect of phosphorus (P) on the toxicity of zinc (Zn) for the alga Raphidocelis subcapitata. P was provided in three concentrations: 2.3 x 10-4 mol L-1, 2.3 x 10-6 mol L-1 and 1.0 x 10-6 mol L-1. Algal cells were acclimated to the specific P concentrations before the start of the experiment. The chemical equilibrium software MINEQL+ 4.61 was employed to calculate the Zn2+ concentration. After acclimated, the algal cells were inoculated into media containing different Zn concentrations (0.09 x 10-6 mol L-1 to 9.08 x 10-6 mol L-1). The study showed that besides the reduction in algal growth rates, phosphorus had an important influence on the toxicity of zinc for microalga. The inhibitory Zn2+ concentration values for R. subcapitata were 2.74 x 10-6 mol L-1, 0.58 x 10-6 mol L-1 and 0.24 x 10-6 mol L-1 for the microalgae acclimated at P concentrations of 2.3 x 10-4 mol L-1, 2.3 x 10-6 mol L-1 and 1.0 x 10-6 mol L-1, respectively. Ecotoxicological studies should consider the interaction between metal concentrations and varying P values to provide realistic data of what occurs in phytoplankton communities in environments.

Sensitivity of the Predictability of Chemical Equilibrium Software to the Choice of the Products

Over the past few decades, researchers have been developing tools to predict chemical reactions to aid the growing field of industrial chemistry. Currently, a large variety of numerical tools are used to predict the final chemical equilibrium based on the minimization of the Gibbs free energy. Due to the mathematical complexity of this problem, numerical methods were developed to solve this problem. These methods were reviewed in another study (CIRCE, A New Software to Predict the Steady State Equilibrium of Chemical Reactions. Comput. Chem. Eng 2018, submitted for publication) exhibiting their limitations and proposing an alternative. In this study, the sensitivity of the prediction to the choice of the most likely products is investigated. In this work, the impact of an improper choice of the final product is investigated showing a first order influence when a product is missing. A method is devised to generate automatically an exhaustive list of final products. Another method is proposed to select in t...

Defluoridation by magnesia–pullulan: Surface complexation modeling and pH neutralization of treated fluoride water by aluminum

Abstract The magnesia–pullulan composite (MgOP) achieved effective fluoride removal in previous research. In the present study, an acid-base titration experiment was conducted to investigate the properties of MgOP surface and further explore the mechanism of fluoride adsorption on MgOP. Results showed that the presence of chloride ions could improve fluoride adsorption on MgOP; however, additional nitrate ions had negligible impacts. A diffuse layer model and chemical equilibrium software (Visual MINTEQ 3.1) were used to simulate the acid-base titration data. The effects of initial pH values on the rate of fluoride uptake by MgOP were also studied. Moreover, aluminum salts were added to the fluoride solution with MgOP for the pH neutralization of treated water, in which aluminum chloride was preferred.

MINFIT: A Spreadsheet-Based Tool for Parameter Estimation in an Equilibrium Speciation Software Program.

Determination of equilibrium constants describing chemical reactions in the aqueous phase and at solid-water interface relies on inverse modeling and parameter estimation. Although there are existing tools available, the steep learning curve prevents the wider community of environmental engineers and chemists to adopt those tools. Stemming from classical chemical equilibrium codes, MINEQL+ has been one of the most widely used chemical equilibrium software programs. We developed a spreadsheet-based tool, which we are calling MINFIT, that interacts with MINEQL+ to perform parameter estimations that optimize model fits to experimental data sets. MINFIT enables automatic and convenient screening of a large number of parameter sets toward the optimal solutions by calling MINEQL+ to perform iterative forward calculations following either exhaustive equidistant grid search or randomized search algorithms. The combined use of the two algorithms can securely guide the searches for the global optima. We developed interactive interfaces so that the optimization processes are transparent. Benchmark examples including both aqueous and surface complexation problems illustrate the parameter estimation and associated sensitivity analysis. MINFIT is accessible at http://minfit.strikingly.com .

Chemical behavior of Cu, Zn, Cd, and Pb in a eutrophic reservoir: speciation and complexation capacity.

This research aimed at evaluating cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) speciation in water samples as well as determining water quality parameters (alkalinity, chlorophyll a, chloride, conductivity, dissolved organic carbon, dissolved oxygen, inorganic carbon, nitrate, pH, total suspended solids, and water temperature) in a eutrophic reservoir. This was performed through calculation of free metal ions using the chemical equilibrium software MINEQL+ 4.61, determination of labile, dissolved, and total metal concentrations via differential pulse anodic stripping voltammetry, and determination of complexed metal by the difference between the total concentration of dissolved and labile metal. Additionally, ligand complexation capacities (CC), such as the strength of the association of metals-ligands (logK'ML) and ligand concentrations (C L) were calculated via Ruzic's linearization method. Water samples were taken in winter and summer, and the results showed that for total and dissolved metals, Zn > Cu > Pb > Cd concentration. In general, higher concentrations of Cu and Zn remained complexed with the dissolved fraction, while Pb was mostly complexed with particulate materials. Chemical equilibrium modeling (MINEQL+) showed that Zn(2+) and Cd(2+) dominated the labile species, while Cu and Pb were complexed with carbonates. Zinc was a unique metal for which a direct relation between dissolved species with labile and complexed forms was obtained. The CC for ligands indicated a higher C L for Cu, followed by Pb, Zn, and Cd in decreasing amounts. Nevertheless, the strength of the association of all metals and their respective ligands was similar. Factor analysis with principal component analysis as the extraction procedure confirmed seasonal effects on water quality parameters and metal speciation. Total, dissolved, and complexed Cu and total, dissolved, complexed, and labile Pb species were all higher in winter, whereas in summer, Zn was mostly present in the complexed form. A high degree of deterioration of the reservoir was confirmed by the results of this study.

Optimizing Metal-Removal Processes for Produced Water With Electrocoagulation

The combination of advances in hydraulic-fracturing and horizontal-drilling technologies has led to a resurgence in oil and gas activity in multiple regions across the United States. To minimize the impact of the increased water use, many oil and gas companies are pursuing fracture-flowback-water and produced-water recycling for subsequent drilling and fracturing operations. Common processes in a recycling strategy include metal precipitation to minimize scaling potential and electrocoagulation for removing solids that may foul a well when water is reused. In this study, precipitation of calcium, magnesium, barium, and strontium were examined experimentally by adding target ligands followed by solids separation with electrocoagulation. In addition, removal efficacy was modeled using commercially available chemical-equilibrium software (OLI Systems). The experimental results were compared with the predicted data at pH values of 9.5 and 10.2. The differences between the modeled data and the experimental data indicated a deficiency in the solid/liquid-separation process in the laboratory. Results also showed that the pH value did not affect the treatment efficiency, except in the case of magnesium; however, sequencing of softening relative to coagulation was important. An additional finding was that, on the basis of the target metal, either sulfate or carbonate needs to be greater than a threshold concentration to achieve precipitation goals. Chemical consumption at pH values of 9.5 and 10.2 was significantly different. Chemical-equilibrium modeling predicts that the average base usage was 30% lower at a pH of 9.5 compared with a pH of 10.2 and 34% lower for acid usage. The reduction in use experimentally was 27% for base and 43% for acid.

Joint toxicity of tetracycline with copper(II) and cadmium(II) to Vibrio fischeri: effect of complexation reaction.

Co-contamination of antibiotic and heavy metals commonly occurs in the environment. Tetracycline (TC), a common antibiotic, can behave as an efficient organic ligand to complex with cations. In this paper, the joint toxicity of TC with two commonly existing metals, copper(II) and cadmium(II), towards a luminescent bacteria, Vibrio fischeri, are investigated. Results showed that coexistence of TC and Cu(II) showed a significant antagonistic effect, while TC and Cd(II) showed a synergistic effect. The aqueous speciation of TC with two metal cations was calculated using a chemical equilibrium software Visual MINTEQ and results indicated that a strong complexation exist between TC and Cu(II), while much weaker interaction between TC and Cd(II). Traditional joint toxicity prediction model based on independent action failed to predict the combined toxicity of TC with metals. A new method based on speciation calculation was used to evaluate the joint toxicity of ligands and cations. It is assumed that the metal-ligand complexes are non-toxic to V. fischeri and the joint toxicity is determined by the sum of toxic unit of free metal-ions and free organic ligands. It explained the joint toxicity of the mixed systems reasonably well. Meanwhile, citric acid (CA) and fulvic acid (FA) were also introduced in this study to provide a benchmark comparison with TC. Results showed it is also valid for mixed systems of CA and FA with metals except for the Cd-CA mixture.

Risk assessment of metal species in sediments of the river Ganga

The present study deals with the geochemical fractions of nine heavy metals [chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd) and lead (Pb)] present on the river sediments using sequential extraction process (SEP) and total acid digestion (TAD). This work was conducted on Ganga river sediments at Varanasi. A ten kilometer stretch of the river Ganga from Samne Ghat to Varuna-Ganga confluence was selected to perform this study. Pollution Load Index (PLI) varied from 1.2 to 3. Geo-accumulation index (Igeo) and Risk Assessment Code (RAC) showed higher concern for Cd and Pb whereas Mn, Fe and Ni showed negative accumulation index at all sampling stations. Lead, cadmium, copper and nickel were present significantly in available fraction; however, the Igeo of Ni was found negative at all stations. Various sources of the metal pollution in the city include domestic, industrial and agricultural untreated wastewater draining into the river. Geochemical fractions of the metals–pH relation study, using Medusa Hydra chemical equilibrium software, revealed the presence of different species of metals at different pHs.

Regeneration of Used Alkali Carbonates for Gaseous Sulfur Removal in a Gasification System

Integrated coal gasification combined cycle is expected to play an important role as one of a number of highly efficient conversion technologies for carbonaceous resources. However, it is vital to remove as much H2S and COS as possible. Our previous study suggested that the molten alkali carbonates of 43 mol of Na2CO3 + 57 mol of K2CO3 can completely adsorb them at 1173 K to form alkali sulfides. Furthermore, to enhance the overall efficiency in the gasification system, the regeneration characteristics of the used alkali carbonates should be studied. Therefore, the current study works on that issue. The optimum regeneration condition for experiments was estimated by chemical equilibrium software, FactSage 6.2, prior to the regeneration experiments. Chemical equilibrium calculations suggested that a mixture of carbon dioxide and steam could regenerate the used alkali carbonates. The experiments were conducted in an electrically heated tube reactor using a mixture of CO2 and steam as the regeneration agent....

Coupling mass transport and chemical equilibrium models for improving the prediction of SWRO permeate boron concentrations

A new simulation approach is presented for predicting boron concentrations in the product water of seawater reverse osmosis operations. The new (numerical) approach links traditional mass-transfer models (the solution–diffusion transport approach and the concentration polarization film-layer model) with full aqueous-phase thermodynamic species characterization, performed by chemical equilibrium software (PHREEQC), based on the Pitzer approach. The new approach results in a more accurate calculation of the boric acid (B(OH)3) molar fraction which develops close to the membrane wall, on the feed side, thereby improving the prediction accuracy of B(OH)3 permeation. Specifically, acknowledging that the pH value of the feed invariably changes as seawater brine progresses through the membranes' train, calculation of this pH change, as performed in the new approach, enables a more physically-accurate and better simulation of the boric acid fraction. The new approach is shown in the paper to result in a prediction that matches better empirical results obtained from the operation of a pilot-scale SWRO plant, as compared to the traditional approach.