Equilibrium and kinetic studies of phosphate removal from solution onto a hydrothermally modified oyster shell material

Insights into kinetics and equilibrium of methylene blue adsorption onto β-cyclodextrin polymers

The exclusive properties of β-cyclodextrin (β-CD) combined with its harmless characters making it as an interesting and potential carbon adsorbent for water pollutants removal via adsorption. This work was aimed at evaluating the kinetics and isotherm parameters of methylene blue dye adsorption onto β-CD polymers. The carbon polymers were prepared by citric acid cross-linking, followed by post-treatment with sodium p-toluenesulfinate. The adsorbents were characterized using TGA, BET and FTIR. The adsorption of methylene blue was studied at varying concentrations (5–300 mg/L) and contact times (10–2880 min), and the kinetics and isotherm models were employed to describe the adsorption data. The post-treated carbon polymer exhibits a greater specific surface of 16.6 m2/g. The maximum adsorption of methylene blue by cross-linked and post-treated β-CD adsorbents are 263 and 227 mg/g, respectively. The kinetics data fitted well into pseudo-first order model, indicating physical adsorption. The Boyd’s model showed that film diffusion may be the controlling mechanism. The equilibrium data of methylene blue adsorption for the two β-CD polymers obeyed Langmuir model. To conclude, β-CD is a promising adsorbent candidate for the treatment of dye wastewater.

Preparation of a novel non-burning polyaluminum chloride residue(PACR) compound filler and its phosphate removal mechanisms

As an inevitable industrial by-product, polyaluminum chloride residue (PACR) will cause serious harm to the environment if directly buried and dumped. The aim of this paper was searched a new economical, environmental, and practical way of utilization for PACR. In this paper, a novel non-burning PACR compound filler was made from mainly PACR. The prepared compound filler has excellent physical properties and phosphate adsorption efficiency of up to 99.9%. Static adsorption experiments showed that the adsorption process of phosphorus by the compound filler conformed to the pseudo-second-order kinetic model and intra-particle diffusion model. Langmuir and Freundlich isotherm models described the phosphorus adsorption process well, and the maximum phosphate adsorption capacity arrived at 42.55 mg/g. The phosphate adsorption by the compound filler is a spontaneous endothermic process. The main mechanisms are ligand exchange and Lewis acid-base interactions; calcium and aluminum play important roles in the adsorption of phosphorus by the compound filler. Dynamic column experiments showed that as much as 90% of the phosphorus removal by compound filler, and the phosphorus concentration decreased from 1 to ~0.1mg/L. The results provide a new waste resource utilization method for PACR and show the good application potential of prepared compound filler in constructed wetlands.

Adsorptive Removal of Phosphate from Aqueous Solutions Using Low-Cost Volcanic Rocks: Kinetics and Equilibrium Approaches

The contamination of surface and groundwater with phosphate originating from industrial and household wastewater remains a serious environmental issue in low-income countries. Herein, phosphate removal from aqueous solutions was studied using low-cost volcanic rocks such as pumice (VPum) and scoria (VSco), obtained from the Ethiopian Great Rift Valley. Batch adsorption experiments were conducted using phosphate solutions with concentrations of 0.5 to 25 mg·L⁻¹ to examine the adsorption kinetic as well as equilibrium conditions. The experimental adsorption data were tested by employing various equilibrium adsorption models, and the Freundlich and Dubinin-Radushkevich (D-R) isotherms best depicted the observations. The maximum phosphate adsorption capacities of VPum and VSco were calculated and found to be 294 mg·kg⁻¹ and 169 mg·kg⁻¹, respectively. A pseudo-second-order kinetic model best described the experimental data with a coefficient of correlation of R² > 0.99 for both VPum and VSco; however, VPum showed a slightly better selectivity for phosphate removal than VSco. The presence of competitive anions markedly reduced the removal efficiency of phosphate from the aqueous solution. The adsorptive removal of phosphate was affected by competitive anions in the order: HCO₃⁻ >F⁻ > SO₄⁻² > NO₃⁻ > Cl⁻ for VPum and HCO₃⁻ > F⁻ > Cl⁻ > SO₄⁻² > NO₃⁻ for VSco. The results indicate that the readily available volcanic rocks have a good adsorptive capacity for phosphate and shall be considered in future studies as test materials for phosphate removal from water in technical-scale experiments.

Kinetics, thermodynamics and mechanisms of phosphate sorption onto bottle gourd biomass modified by (3-chloro-2-hydroxypropyl) trimethylammonium chloride

The sorption kinetics and thermodynamic parameters of phosphate removal from aqueous solution using quaternary ammonium–modified bottle gourd biomass as a sorbent were studied in a batch reactor. The cationic sorbent, containing trimethylammonium and hydroxypropyl groups, was obtained through the chemical reactions of the lignocellulosic Lagenaria vulgaris shell with (3-chloro-2-hydroxypropyl)trimethylammonium chloride. Experimental data of phosphate sorption from aqueous solutions of different initial concentrations (5–140 mg P L−1) have been analysed by reaction kinetics and diffusion models. The characteristic rate constants calculated by linear and non-linear regression analyses of the experimental results are presented. The phosphate sorption reaches equilibrium in 20–30 min, depending on the initial phosphate concentration. The maximum sorption capacity of quaternary ammonium–modified bottle gourd (QABG) sorbent was 18 mg P g−1 at 20 oC. The sorption system is best described by a non-linear equation of the pseudo first-order model ( R2 > 0.996). The Weber–Morris model indicated that the sorption process took place in three steps, whereby the intra-particle diffusion is not the only rate-controlling step. In addition, the effect of temperature (20 oC–50 oC) on sorption kinetics was also investigated. The various thermodynamic parameters suggest that phosphate sorption is favoured and is an exothermic process. The activation energy and the sticking probability confirmed that anion exchange is the dominant mechanism. These results provide valuable information for the potential use of agricultural residues in the treatment of wastewaters.

Preparation of sustainable non-combustion filler substrate from waterworks sludge/aluminum slag/gypsum/silica/maifan stone for phosphorus immobilization in constructed wetlands

In this study, an artificial wetland filler matrix capable of effectively fixing phosphorus was prepared using a non-combustion process to save energy. To evaluate the adsorption performance of this filler, adsorption experiments were performed and the phosphorus adsorption mechanism characterization was studied. An alkaline environment was found to be conducive to the increase of adsorption capacity, but excessive alkalinity was not conducive to adsorption. Static adsorption experiments showed that the phosphorus removal rate could reach 95% in the simulated phosphorus-containing wastewater after adsorption completion. The adsorption process is closely simulated by the pseudo-second-kinetic adsorption model. The isothermal adsorption experiment data were consistent with the Langmuir and the Freundlich adsorption isotherms. The characterization results showed a large number of micropores and adsorption binding sites inside and on the surface of the filler. Speciation analysis on the adsorbed phosphorus revealed that chemisorption by calcium in this filler was the dominant adsorption mechanism. The research results of this study provide the basis and reference for the development of high-efficiency phosphorus removal filler in constructed wetlands.

Calcined Eggshell as a P Reactive Media Filter-Batch Tests and Column Sorption Experiment

The goal of the study was to assess the sorption properties of calcined eggshells (CEs) as a P reactive media filter. The CEs were calcined in a temperature of 900 °C. A double stage test was performed: batch studies (kinetic and equilibrium) and small-scale column experiment. The estimation of optimal mass ratio of CEs for perspective usage was the additional benefit of column experiment. The short kinetic tests showed that 5 min of contact time with solution of initial concentration of 6.020 mgP-PO₄ L^-1 is enough to reduce the P-PO₄ in 100%. The equilibrium studies were conducted with P-PO₄ solution of 6.020 to 977.7 mg L^-1 with contact time of 30 min. The obtained data was compensated by non-linear regression using the Marquardt algorithm in the Statgraphics Centurion XVI. The eggshell calcined characterized by high sorption capacity (S _max = 72.87 mg g^-1) obtained from the Langmuir isotherm model with a good fit (96.77%). To choose the appropriate ratio of a sand filter to eggshells amendment, four small columns were constructed and fed with P-PO₄ solution (C _in ≈ 5 mg L^-1). The percentage mass (m/m) of CEs in the columns was 0.0 (the reference one); 1.0; 2.5; and 5.0. The unit sorption obtained during 95 days of column experiment was 10.668, 4.277, and 2.286 mg P-PO₄ g^-1 for 1.0, 2.5, and 5.0%, respectively. For practical implementation, the most recommended addition seems to be 1% of CEs. It corresponds, e.g., to the mass of 49 kg CEs for septic tank system.

Synthesis and Adsorption Properties of Hierarchically Ordered Nanostructures Derived from Porous CaO Network

Using the porous framework of CaO as templates and reagents, we explored a surfactant-free and economical method for preparing calcium silicate hydrate (CSH) hierarchically ordered nanostructures. Incorporation of SiO₂ nanoparticles into the CaO framework, followed by a reaction assisted by hydrothermal treatment, resulted in the formation of CSH with well-defined morphologies. The structural features of CSH were characterized by 3-D hierarchical networks, wherein nanofibers assembled to form nanosheets, and nanosheets assembled to form hierarchically ordered structures. Investigation of the crystal growth mechanism indicated that the key to forming the CSH ordered assembly structure was confining the Ca/Si ratio within a small range. Nonclassic oriented aggregation mechanism was used to describe the crystal growth of nanosheets, while the porous CaO framework served as template/reagents responsible for the formation of hierarchical structures. The resulting CSH adsorbent exhibited better performance in removing Pb(II) compared with other types of random CSH adsorbents. Additionally, the hierarchical structure of CSH provided more pores and active sites as support for other active functional materials such as zerovalent iron (Fe⁰). As-produced CSH@Fe nanocomposite with self-supported structures displayed high capacities for removal of Pb(II) after five adsorption-desorption cycles, and high capacities for other heavy metal ions (Cu²⁺, Cd²⁺, and Cr₂O₇^2-) and organic contaminants.

Kinetics and Mechanisms of Phosphorus Adsorption in Soils from Diverse Ecological Zones in the Source Area of a Drinking-Water Reservoir

On-site soils are increasingly used in the treatment and restoration of ecosystems to harmonize with the local landscape and minimize costs. Eight natural soils from diverse ecological zones in the source area of a drinking-water reservoir in central China are used as adsorbents for the uptake of phosphorus from aqueous solutions. The X-ray fluorescence (XRF) spectrometric and BET (Brunauer-Emmett-Teller) tests and the Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FTIR) spectral analyses are carried out to investigate the soils' chemical properties and their potential changes with adsorbed phosphorous from aqueous solutions. The intra-particle diffusion, pseudo-first-order, and pseudo-second-order kinetic models describe the adsorption kinetic processes. Our results indicate that the adsorption processes of phosphorus in soils occurred in three stages and that the rate-controlling steps are not solely dependent on intra-particle diffusion. A quantitative comparison of two kinetics models based on their linear and non-linear representations, and using the chi-square (χ2) test and the coefficient of determination (r2), indicates that the adsorptive properties of the soils are best described by the non-linear pseudo-second-order kinetic model. The adsorption characteristics of aqueous phosphorous are determined along with the essential kinetic parameters.

Enhanced removal of diclofenac from water using a zeolitic imidazole framework functionalized with cetyltrimethylammonium bromide (CTAB)

A cationic surfactant, CTAB, is introduced to ZIF-67 to enhance the adsorption capacity for one of the most common PPCPs, diclofenac sodium.