Freundlich Parameters Research Articles

Enhanced phosphorus adsorption using modified drinking water treatment residues: A comparative analysis of powder and alginate bead forms

This study provides an analysis of the phosphorus adsorption efficacy of three modified drinking water treatment residues (MDWTRs): MDWTR-P (powdered form), MDWTR-D2, and MDWTR-D5 (alginate bead-entrapped forms with bead diameters of 2 mm and 5 mm, respectively). The preparation process involved washing and drying the drinking water treatment residue, followed by grinding and sieving to achieve particle sizes below 90 μm. The residue was then incinerated at 600 °C in oxygen-limited conditions. Subsequently, the MDWTR was formulated into alginate beads by mixing with sodium alginate and FeCl3 solutions, resulting in spherical particles of specified diameters. The evaluation of surface area, pore volume, pore size, and CHN concentration revealed that MDWTR-D5 possesses the largest surface area (284.7 m2 g−1) and highest micropore volume (0.04 cm3 g−1), indicating a greater capacity for adsorption. SEM-EDS analysis demonstrated significant compositional changes post-treatment, particularly elevated phosphorus levels, confirming effective adsorption. Metal content analysis indicated high aluminum levels in MDWTR-P and increased iron content in MDWTR-D5. Toxicity Characteristic Leaching Procedure (TCLP) and in vitro bioaccessibility (IVBA) tests confirmed the non-hazardous nature of all MDWTRs, ensuring their safety for environmental applications. Kinetic analyses using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models highlighted the superior performance of MDWTR-D5, with the highest equilibrium adsorption capacity and initial adsorption rate across all tested concentrations, suggesting both high efficiency and rapid adsorption potential. Further validation using Langmuir and Freundlich isotherms revealed MDWTR-D5's highest monolayer adsorption capacity (22.88 mg g−1) and Freundlich adsorption capacity parameter (6.97 mg g−1). Statistical analysis via one-way ANOVA confirmed significant differences in phosphorus concentrations among the MDWTRs samples (p-value <0.001), consistently underscoring MDWTR-D5's superior adsorption performance. These findings highlight MDWTR-D5's potential as an effective adsorbent for phosphorus removal in wastewater treatment, emphasizing its applicability in environmental remediation strategies.

Effect of Low Molecular Weight Organic Acids and Liming on Phosphorus Adsorption in Acidic Tea Soils in the Black Sea Region, Türkiye

ABSTRACT Agricultural productivity is significantly hindered by the limited availability of phosphorus in acidic soils due to the presence of aluminum and iron phosphates. Soil liming is commonly employed to enhance soil fertility. However, modifying the pH might also impact the interactions involving existing soil organic matter, leading to changes in the effective concentrations of competing low-molecular-weight acids (LMWOACs) participating in phosphorus adsorption. This study explored the impacts of citric, oxalic, and malic acids in acidic soils from tea cultivation regions within the Eastern Black Sea. These soils had undergone various levels of liming and were incubated for 15 months to assess their effects on phosphorus (P) adsorption in 7 acidic soils. The experimental sorption data were utilized to calculate the soil Langmuir and Freundlich adsorption parameters. In addition, the influences of organic acids and liming levels on the Freundlich and Langmuir model parameters were subjected to ANOVA analysis. The findings indicated that citric acid demonstrated the highest efficiency in diminishing phosphorus adsorption among the tested organic acids, followed by oxalic and malic acids. Three carboxyl groups (−COOH) in citric acid facilitated the formation of more complexes with adsorbed phosphorus on the soil surface. Furthermore, the 100% LR ratio of liming notably decreased phosphorus adsorption, especially in the lower end of the isotherms. Therefore, it can be concluded that the combination of LMWOACs and liming treatments could be used to overcome P deficiency in acid soils with very high P sorption ability.

Biosorption of Cd(II), Co(II), and Cu(II) onto Microalgae under Acidic and Neutral Conditions

The biosorption of Cd, Co, and Cu onto three microalgae species (Chlorella vulgaris, Scenedesmus sp., and Spirulina platensis) was compared to determine the microalgae’s capability for heavy metal adsorption in acidic and neutral environments. The Langmuir, Freundlich, and Dubinin–Radushkevich isotherm models were used to characterize the adsorption of the heavy metals onto microalgae. The maximum adsorption capacity (qmax) determined using the Langmuir and D-R model showed results in the order of Cu &gt; Co &gt; Cd in both acidic and neutral conditions. A shift from acidic to neutral conditions increased the microalgae’s adsorption affinity for heavy metals, as determined using the Freundlich parameter (KF). The adsorption affinity of the biomass for Cd and Co was in the order S. platensis &gt; C. vulgaris &gt; Scenedesmus sp. while that of Cu was in the order C. vulgaris &gt; Scenedesmus sp. &gt; S. platensis. In addition, it was found that the adsorption of Cd and Co enhanced the production of Dissolved Organic Content (DOC) as a byproduct of biosorption, whereas the adsorption of Cu appeared to suppress the generation of DOC. The mean adsorption energy (E) values computed by the D-R model were less than 8 (kJ/mol), indicating that physisorption was the primary force of sorption in both acidic and neutral settings. The findings of this study suggest that microalgae may be used as a low-cost adsorbent for metal removal from industrial effluent.

Effect of soil organic amendments on sorption behavior of two insecticides and two herbicides

The effect of biochar, compost, peat and wheat straw at 1 and 5% on adsorption isotherm of chlorantraniliprole, dinotefuran, bispyribac-sodium, and metribuzin was studied in clay loam soil and sandy loam soil. Biochar, compost, peat and wheat straw (at a rate of 1 % in soil) improved the adsorption capacity of chlorantraniliprole and metribuzin in sandy loam soil. The sorption coefficients are higher for chlorantraniliprole and metribuzin whereas lower for dinotefuran and bispyribac-sodium in amended soil compared to unamended sandy loam soil. There is not a clear direct correlation between Freundlich parameters as well as Kd or Koc and type of organic amendment. The sorption of all tested pesticides on biochar was increased, whereas on compost was decreased. The order of pesticides sorption in soils and different organic amendments is generally inversely proportional to their aqueous solubilites. Adsorption of chlorantraniliprole increases on the sandy loam soil amendment at the rate of 1% in the following order: peat &gt; compost &gt; biochar &gt; original soil. Also, the magnitude of adsorption on soil A amendment at the rate of 5% can be arranged for dinotefuran in the order; peat &gt; biochar &gt; compost &gt; original soil and for bispyribac-sodium and metribuzin peat = wheat straw &gt; biochar &gt; original soil.

Equilibrium, kinetics, and thermodynamics of batch adsorption of Mn(II) ions on blast furnace slag (BFS) and kaolin (KGA)

This article describes the discontinuous adsorption of Mn(II) on kaolin from Guelma, Algeria (KGA), and blast furnace slag from Sider, Algeria (BFS), under the effect of various parameters, namely the contact time, the stirring speed, the pH of the medium, the solution temperature, the adsorbent dosage, the solid particle size, and the initial concentration. Also studied were the models of adsorption, namely the isotherms of adsorption, the kinetics of adsorption, and the thermodynamic study of Mn on the examined adsorbents. Characterization tests have indicated that kaolin consists essentially of hydrated aluminum silicate. The BFS is mainly composed of silicates, aluminates, lime, and magnesium oxide. The specific surface areas of kaolin and BFS calculated using the BET were defined at 134.2 and 238.6m2/g. The adsorption rate of Mn(II) on KGA and BFS is better after 50 and 60 min of contact at Vag: 150 rpm; pH: 5.2; Øs: 100 μm; T: 20 °C; Ms: 1 g, respectively. Maximum adsorption capacities are 36.76 mg/g (KGA) and 59.88 mg/g (BFS). Examination of the adsorption isotherms revealed that the Langmuir model is more appropriate to the experimental data (R2 = 0.99). The values of the Freundlich (n), Langmuir (RL), and Temkin (bt) parameters indicate that the adsorption is favorable. The kinetic examination demonstrated that the pseudo-second-order kinetic model is more adopted for the adsorption of Mn(II) on KGA and BFS (R2 = 0.99). Furthermore, the transfer of Mn(II) from the solution to the surfaces of the investigated adsorbents is controlled by external and internal diffusion. The thermodynamic study brought to light that the adsorption processes carried out were spontaneous, exothermic, and less entropic. This work showed that KGA and BFS can be used as low-cost adsorbents for the removal of Mn(II) ions in aqueous media, and BFS has higher affinities for manganese ion adsorption.

Polanyi adsorption potential theory for estimating PFAS treatment with granular activated carbon

Per- and polyfluoroalkyl substances (PFAS) are a group of chemicals that have gained interest because some PFAS have been shown to have negative health effects and prolonged environmental and biological persistence. Chemicals classified as PFAS have a wide range of chemical moieties that impart widely variable properties, leading to a range of water treatment process efficacies. The Polanyi Potential Adsorption Theory was used to estimate Freundlich isotherm parameters to predict the efficacy of granular activated carbon (GAC) treatment for 428 PFAS chemicals for which the vast majority had no previously published treatment data. This method accounts for the physical/chemical characteristics of the individual PFAS beyond molecular weight or chain length that have previously been employed. From a statistical analysis of available data and model results, many of the 428 PFAS were predicted to be effectively treatable by GAC. Although not directly applicable to full-scale design, the approach demonstrates a systematic method for predicting the effectiveness of GAC where isotherm or column data are not available. This then can be used to prioritize future research.

Contaminant retention affected by controlled and uncontrolled pH for fly ash-bentonite composites used as landfill liner material

Contaminant retention characteristics of clay-based composites as affected by pH needs to be quantified for its design, functionality, and performance as a landfill liner material. The efficacy of four fly ash (FA) in bentonite-fly ash (B-FA) mixes was investigated for its lead (Pb2+) retention characteristics under controlled pH (pH = 5) and realistic uncontrolled pH conditions anticipated in the landfill liners. B-FA mixes with 30%, 50%, and 70% FA amendment, bentonite-sand (B–S) mixes, and parent materials were tested by batch sorption tests. Under uncontrolled pH conditions, the retention capacity of all parent materials and mixes was higher than the controlled pH condition due to significant precipitation reaction and complexation associated with pH. Beyond 1000 mg.L-1 initial concentration, B-FA mixes constituting FA with inherent pH > 10.5 were the most efficacious adsorbents. Under both pH conditions, the metal retention capacity of B-FA mixes was higher than that of conventional B-sand mixes. All results were analytically substantiated by detailed FESEM micrographs, XRD, and EDX spectra of samples before and after sorption. The Freundlich and Langmuir nonlinear retention model parameters indicate that the uncontrolled pH condition results in nonlinear sorption, the higher energy of sorption, and stronger interactive bonds between Pb2+ ions and sorbent.

Yesterday, Today, and Tomorrow. Evolution of a Sleeping Beauty: The Freundlich Isotherm.

The name of Herbert Freundlich is commonly associated with a power relationship for adsorbed amount of a substance (Cads) against the concentration in solution (Csln), such that Cads = KCslnn; this isotherm (together with the Langmuir isotherm) is considered to be the model of choice for correlating the experimental adsorption data of micropollutants or contaminants of emerging concern (pesticides, pharmaceuticals, and personal care products), but it also concerns the adsorption of gases on solids. However, Freundlich's 1907 paper was a "sleeping beauty", which only started to attract significant citations from the early 2000s onward; moreover, these citations were too often wrong. In this paper, the main steps in the historical developments of Freundlich isotherm are identified, along with a discussion of several theoretical points: (1) derivation of the Freundlich isotherm from an exponential distribution of energies, leading to a more general equation, based on the Gauss hypergeometric function, of which the power Freundlich equation is an approximation; (2) application of this hypergeometric isotherm to the case of competitive adsorption, when the binding energies are perfectly correlated; and (3) new equations for estimating the Freundlich coefficient KF from physicochemical properties such as the sticking surface or probability. From new data treatment of two examples from the literature, the influence of several parameters is highlighted, and the application of linear free-energy relationships (LFER) to the Freundlich parameters for different series of compounds is evoked, along with its limitations. We also suggest some ideas that may be worth exploring in the future, such as extending the range of applications of the Freundlich isotherm by means of its hypergeometric version, extending the competitive adsorption isotherm in the case of partial correlation, and exploring the interest of the sticking surfaces or probabilities instead of KF for LFER analysis.

Cu(II) Removal from Aqueous Medium Using Blast Furnace Slag (BFS) as an Effective Adsorbent

The copper adsorption by blast furnace slag (BFS) in an aqueous medium was considered based on the influencing parameters, namely the agitation speed, pH, temperature, the particle size of the solid, and the initial concentration. Physicochemical studies have shown that BFS is consisted mainly from SiO2, CaO, Al2O3, and MgO with a specific surface area of 238 m2/g. Under the optimum parameters, the maximum adsorption amount at equilibrium (140 min) corresponds to 45.16 mg/g. Exploration of adsorption isotherms revealed that the Langmuir model is more consistent with the experimental data. The values of the Freundlich (n) and Langmuir (RL) parameters indicate that the adsorption is favorable. On the other hand, the values of Temkin (bt) and Redlich-Peterson (g) parameters show that adsorption is physical. Pseudo-second order of the adsorption process was confirmed using a kinetic study. Moreover, the diffusional study specified that the transfer of copper from the solution to BFS is successively controlled by external and intraparticle diffusion. The thermodynamic parameters showed that the adsorption of Cu(II) on BFS was feasible, spontaneous, exothermic, and less entropic. The desorption phenomenon has revealed that BFS can be reused for three consecutive cycles.

Fate and Transport of Lead and Copper in Calcareous Soil

Heavy metals transport to groundwater relies on the characteristics of soil, such as carbonate and clay minerals, organic matter content, soil pH, and some other factors. Most of the heavy metals in calcareous soils are precipitated as metal carbonate minerals; consequently, their transport to the groundwater is not anticipated. Therefore, the current study focused on the impacts of calcium carbonate presence on the adsorption and transport of lead (Pb) and copper (Cu) in calcareous soil using batch and column experiments. To elucidate the contaminants removal mechanisms in calcareous soils, extensive laboratory batch investigations were conducted to study the equilibrium kinetic and adsorption isotherm characteristics of the two studied heavy metals. The quick adsorption of Pb2+ and Cu2+ by soil was seen in kinetics trials. In addition, Pb2+ and Cu2+ sorption onto the soil was best described by the pseudo-second order kinetic model (R2 = 0.9979 and 0.9995 for Cu2+ and Pb2+, respectively). To explain the equilibrium sorption data, the Freundlich isotherm showed the best fitness to Pb2+ (R2 = 0.96) and Cu2+ (R2 = 0.98), collectively. The Freundlich parameters revealed that the Pb2+ has favorable adsorption; however, Cu2+ has unfavorable adsorption onto the soil. The results of column experiments showed the higher binding of Pb2+ than Cu2+ to the top surface of the soil column, making the movement of these two metals very slow. In columns, most of the Pb2+ and Cu2+ ions were sorbed at an initial 5 and 10 cm, respectively. The findings of this study will help in understanding the fate of heavy metals in calcareous soils.

Application of isotherm models to combined filter systems for the prediction of iron and lead removal from automobile workshop stormwater runoff

Langmuir and Freundlich isotherm adsorption models were used to predict iron and lead removal from automobile workshop stormwater runoff. Combined low-cost filter systems consisting of granular activated carbon–rice husk (GAC–RH) and river gravel–granular activated carbon (GR–GAC) were used in this study. The effects of adsorbent dosage and contact time on the adsorption capacity of the adsorbents, as well as the removal efficiencies of the adsorbent systems, were also investigated. The results for the Langmuir model generally showed favourable adsorption processes., with all RL values &lt; 1 (in the range 0.358–0.518). The Langmuir model gave better predictions for iron and lead removal, with high R2 values (in the range 0.842–0.969), while the root mean square error (RMSE) values ranged from 0.002 to 2.366. The Freundlich model parameters indicated chemisorption processes with all n values &lt; 1 (in the range 0.1296–0.4675). R2 values were in the range of 0.634–0.916 while RMSE values ranged from 0.002 to 0.1765. Additionally, the removal efficiencies for iron and lead using GAC–RH filter system (54% and 48%, respectively) were found to be higher than those obtained using GR–GAC filter system (35% and 25%, respectively). The adsorption capacities of the adsorbents decreased with increased dosages of the adsorbent, with optimum adsorbent dosage of 0.5 g and equilibrium contact time of 80 min for the combined filter adsorbents. Further research towards modifying adsorbents for removal of oil and grease from polluted automobile workshop stormwater runoff are warranted.

Isothermal Modelling of the Adsorption of Lead (II) Onto Activated Carbon from Tridax procumbens

Hypertension and kidney damage have been linked to lead exposure in adults. Any person can be harmed by lead, but pregnant women and their unborn children are especially vulnerable. Presently, lead pollution is removed using membrane separation, ion exchange, precipitation, and biosorption. Biosorption's low operating costs, high efficiency at detoxifying low concentrations of toxicants, and small volume of disposal materials make it the least problematic of these technologies. The biosorption of lead (II) onto activated carbon from Tridax procumbens is remodeled using nonlinear regression and the optimal mode was determined by a series of error function assessments. The Freundlich model performed best in statistical tests including root-mean-square error (RMSE), adjusted coefficient of determination (adjR2), bias factor (BF), accuracy factor (AF), and corrected Akaike Information Criterion (AICc) The calculated Freundlich parameters kF value using nonlinear regression was 1.334 (1/g) (95% confidence interval from 0.821 to 1.847) and nF value of 3.872 (95% C.I. from 1.972 to 5.771). Modelling using a nonlinear approach allows for the calculation of uncertainty range in terms of 95% confidence interval that would be useful for model comparison and discriminant in future studies

Isothermal Modelling of the Adsorption of Cadmium onto Activated Carbon from Tridax procumbens

There is currently no feasible method of recycling Cd compounds, despite the fact that Cd production, consumption, and environmental release have all skyrocketed in recent decades. This raises serious concerns about the potential dangers of Cd compounds to human health. This highlights the pressing need for cadmium pollution cleanup. Biosorption is one of several viable technologies with several advantages, including low operating costs, very efficient detoxification of toxicants at low concentrations, and a low amount of disposal materials. The biosorption of cadmium onto activated carbon from Tridax procumbens is remodeled using nonlinear regression and the optimal mode was determined by a series of error function assessments. The Freundlich model performed best in statistical tests including root-mean-square error (RMSE), adjusted coefficient of determination (adjR2), bias factor (BF), accuracy factor (AF), and corrected Akaike Information Criterion (AICc). This is in contrast to the published work using a linearized form where the Langmuir model best represents the biosorption. The calculated Freundlich parameters kF value using nonlinear regression was 1.501 (1/g) (95% confidence interval from 1.223 to 1.778) and nF value of 4.943 (95% C.I. from 3.492 to 6.393). Confidence intervals for the uncertainty range can be calculated using nonlinear modeling and then used for model comparison and discriminant analysis.

CAPTURE OF CARBON DIOXIDE FROM SEWAGE SLUDGE PYROLYSIS GASES IN A FIXED BED OF 13X ZEOLITE

Pyrolysis gases can be upgraded through CO2 adsorption. This work shows the pyrolysis of sewage sludge in a 1 kg h−1 rotating cylinder reactor. Non-condensable gases passed through a fixed bed of 13X zeolite at 40 ◦C. Prior to processing actual pyrolysis gases, the equilibrium adsorption capacity of the 13X was evaluated with synthetic CO2 in a magnetic suspension balance to estimate Langmuir, Freundlich and Toth isotherm parameters. Afterwards, a synthetic mixture with composition similar to that of sewage pyrolysis gases was tested in a bench-scale fixed-bed adsorption column to assess both the breakthrough curves for different adsorbent masses (10, 15, and 20 g) and the saturation time of the adsorbent. The dynamic adsorption in the column was modeled as a system of partial differential equations (PDEs), which was transformed into a system of Ordinary Differential Equations (ODEs) via the Method of Lines and, then, solved using DASSL. The ODEs were used to estimate adsorption parameters such as coefficient of axial dispersion, effective diffusivity within the particle, and external coefficient of mass transfer. The synthetic gases were replaced with actual sewage sludge pyrolysis gases in the adsorption column with 13X. The breakthrough curves revealed a quick saturation of the bed by pyrolysis aerosols. Despite its short lifetime in comparison with synthetic gases, the 13X proved effective in adsorbing pyrolysis CO2.

Sulfur Fractions, Distribution and Sorption Characteristics in Some Soils of Ogun State, Southwestern Nigeria

ABSTRACT Sulfur (S) fractions, distributions and sorption characteristics of some soils in Ogunstate, Southwestern Nigeria, were evaluated in ten different locations, the area lies with in the Derived Savannah and forest agro-ecological zone. Result showed available, adsorbed, organic and total S ranged from 3.9 to 19.8, 16.3 to 36.6, 214.9 to 412.9 and 248.8 to 446.6 mg kg−1 respectively. Organic S constituted 86.4 to 93.4% of total S. The mean status of available S was slightly above the critical limit of 10 mg kg−1. All fractions of S maintained significant positive correlation (p ≤ .05) with each other and total organic carbon, while available and adsorbed S had significant and negative correlation with soil pH, total nitrogen, available phosphorus and calcium. The S sorption behavior of the soils varied and increased with increase in S concentrations of equilibrium solution. The isotherm model for the ten locations was S-curved type. Sorption data were fitted to Langmuir and Freundlich sorption isotherms. Langmuir equation was best fitted to the S adsorption data in the ten locations except soils from Owode, Odeda and Ikenne. Langmuir and Freundlich parameters (sorption maxima, binding energy and maximum buffering capacity affinity constant and slope) were significantly correlated with some soil properties.

Adsorption of a cationic dye (Methylene bleu) by Typha Latifolia: Equilibrium, kinetic, thermodynamic and DFT calculations

In this work, the adsorption performance of methylene blue (MB) on rough R and Typha Latifolia RS was studied. On one hand, the effect of various parameters on the adsorption efficiency were studied knowing that the mass of the material, the adsorption time, the initial concentration and the pH of solution. All these different parameters influence the absorption capacity. The maximum amount of adsorption of the different materials studied are estimated at 21.01 mg g−1 and 54.73 mg g−1 at pH = 5. Under all optimal conditions, the relevant MB removal rates at R and RS were 69.62% and 91.09%, respectively. On the other hand, the mathematical modeling studied has shown that the S-type adsorption process and that the pseudo second order and Langmuir are the most suitable models to describe the adsorption of the cationic dye via R and RS. In fact, the study of Langmuir and Freundlich parameters has indicated that the removal of MB by R and RS is favorable. Moreover, Theoretical calculations were carried out using simulations of the (DFT) explored the interaction between the most reactive sites concerning the major biosorbent constituent Typha Latifolia which is the cellulosic polymer and the cationic dye MB. The comparative study of all experimental and theoretical results has confirmed the biosorption potential of the studied biosorbent for the removal of dyes.

Dried Brown Seaweed's Phytoremediation Potential for Methylene Blue Dye Removal from Aquatic Environments.

The dried form of the brown seaweed Sargassum latifolium was tested for its ability to remove toxic Methylene Blue Dye (MBD) ions from aqueous synthetic solutions and industrial wastewater effluents. In a batch adsorption experiment, different initial concentrations of MBD (5, 10, 20, 30, and 40 mg L−1), sorbent dosages (0.025, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 g L−1), contact time (5, 10, 15, 30, 60, 120 min), pH (3, 5, 8, 10, and 12), and temperature (30, 40, 50, 60 °C) were observed. Dried powder of S. latifolium was characterized before and after adsorption of MBD using different techniques, such as FTIR, SEM, UV visible spectral examination, and BET techniques. The BET surface area suggests the formation of S. latifolium was 111.65 m2 g−1, and the average pore size was 2.19 nm. The obtained results showed that at an MBD concentration of 40 mg L−1, the adsorption was rapid in the first 5, 10, and 15 min of contact time, and an equilibrium was reached in about 60 and 120 min for the adsorption. At the optimum temperature of 30 °C and the adsorbent dose of 0.1 g L−1, approximately 94.88% of MBD were removed. To find the best-fit isotherm model, the error function equations are applied to the isotherm model findings. Both Tempkin and Freundlich isotherm models could appropriate the equilibrium data, as well as the pseudo 2nd order kinetics model due to high correlation coefficients (R2). Thermodynamic and Freundlich model parameters were assessed and showed that the mechanism of the sorption process occurs by an endothermic and physical process. According to the results of the experiments, S. latifolium is a promising environmentally friendly approach for eliminating MBD from the aqueous solution that is also cost-effective. This technology could be useful in addressing the rising demand for adsorbents employed in environmental protection processes.

Solid-solution partitioning of micronutrients Zn, Cu and B in tropical soils: Mechanistic and empirical models

Trace elements such as zinc (Zn), copper (Cu) and boron (B) are important micronutrients for crop production. Their bioavailability is essential to crops yield quantity and quality in many tropical soils. Nutrient bioavailability depends partly on the soil nutrient status, and in particular on the reactive and soluble fractions. Adsorption/desorption and precipitation/dissolution processes control the partitioning of the reactive pool over the solid and solution phase. However, so far the solid-solution partitioning of trace elements has mostly been studied in temperate and often contaminated soils. We studied, therefore, the solid-solution partitioning of Zn, Cu and B for 172 soils from Burundi, Rwanda and Kenya, using extensive soil characterization in combination with multi-surface modelling and two types of empirical Freundlich type partition relations. Our aim was to enhance the understanding of the soil chemical processes that control the solid-solution partitioning of the three micronutrients in these soils from the tropics with a multi-surface model, and to use this knowledge as benchmark to develop partition relations that require less input data and are more convenient tools for predicting the concentration in solution based on existing soil data. We show that the generic multi-surface model applied to these tropical soils performs similarly for Zn and Cu as in previous studies on temperate and contaminated soils. The Zn and Cu speciation was dominated by adsorption to soil organic matter, with an increased importance of metal (hydr)oxides with increasing pH. Given its generally low concentrations in these soils, dissolved organic matter was found to be important only for the solution speciation of Cu. The adsorption of B was mainly to metal (hydr)oxides at low pH, and with increasing pH soil organic matter became more important. The multi-surface model overestimated the dissolved B concentration for most soil samples, which we attributed to an inaccurate estimation of reactive B. Interestingly, the variation in observed and modeled solid-solution partitioning expressed as Kd of Cu and B among the soils was relatively small (∼1 log L kg−1), and the concentration in solution was consistently mainly controlled by the reactive concentration. Generally, the optimized partition relations resulted in a smaller prediction error compared to the multi-surface models. The partition relations in which the concentration in solution was optimized, resulted generally in an overestimation for the lowest observed concentrations, and an underestimation for highest concentrations of all three elements. Partition relations with optimized Freundlich parameters Kf and n resulted in more robust predictions since the prediction error was not related to the actual measured concentration. The partition relations from this study are easy-to-use tools for predicting the dissolved concentrations of Zn, Cu and B in soils from the tropics with low contents of these micronutrients and can therefore enhance the use of current existing soil information data for Sub-Saharan Africa.

Fly Ash-Added, Seawater-Mixed Pervious Concrete: Compressive Strength, Permeability, and Phosphorus Removal.

A mix proportion of off-spec fly ash (FA)-added, seawater-mixed pervious concrete (SMPC) was optimized for compressive strength and permeability and then the optimized SMPC was tested for the rate and extent of aqueous phosphorus removal. An optimum mix proportion was obtained to attain the percentages (% wt.) of FA-to-binder at 15.0%, nano SiO2 (NS)-to-FA at 3.0%, liquid-to-binder at 0.338, and water reducer-to-binder at 0.18% from which a 7-day compressive strength of 14.0 MPa and a permeability of 5.5 mm/s were predicted. A long-term maximum compressive strength was measured to be ~16 MPa for both the optimized SMPC and the control ordinary pervious concrete (Control PC). The phosphorus removal was favorable for both the optimized SMPC and the Control PC based on the dimensionless Freundlich parameter (1/n). Both the optimized SMPC and Control PC had a first-order phosphorus removal constant of ~0.03 h−1. The optimized SMPC had a slightly lower capacity of phosphorus removal than the Control PC based on the Freundlich constant, Kf (mg1−1/n kg−1 L1/n): 15.72 for the optimized SMPC vs. 16.63 for Control. This study demonstrates a cleaner production and application of off-spec FA-added, seawater-mixed pervious concrete to simultaneously attain water, waste, and concrete sustainability.

ADSORPTION ISOTHERM MODELS AND KINETICS FOR PHOSPHATE ADSORPTION IN SEDIMENT

Phosphate ions in solution can be adsorbed using sediment. Phosphate adsorption by sediment was influenced by concentration, adsorbent dosage, and temperature. The research was carried out at pH 1 for 30 minutes. The optimum adsorption occurs at a concentration of 15 ppm with an adsorption capacity of 0.41 mg/g. The adsorbent dosage was used as 1 mg with a capacity of adsorption capacity of (0.6077 mg/g). The optimum temperature is obtained at 40oC with a capacity of adsorption (0.1250 mg/g). Adsorption isotherm follows the Langmuir and Freundlich model. The Langmuir parameters as R2 (0.7270) KL(6.1750 L/mg), qm (0.3329 mg/g). Freundlich parameters were obtained as follows: R2 (0.9741), 1/n (0.6059), and KF (0.5635 m/g (L/mg)1/n. Reaction kinetics based on pseudo-second-order kinetic with a value of R2 = 0.9717, K = 25.2554 gmol-1hour-1