Competitive sorption of Cu(II) and Ni(II) ions from aqueous solutions: Kinetics, thermodynamics and desorption studies

Evidence from experiments, modeling, and field observations for effects of increased salinization on re-distribution of sediment base cations in Taihu Lake, China

Taihu Lake, the third largest freshwater lake in China, has experienced rapid salinization in the past decades; however, little is known about the impact of sodium (Na) on ion exchange in the lake environment. To explore the potential effect of increased Na on the migration of base cations (Ca and Mg) and resulting redistribution between the water and sediment, we used the adsorption-exchange experiment, MINTEQ modeling to explore the cation exchange induced by high Na input, and its impact on the redistribution of Ca and Mg in Taihu different media. The results indicated that exchanged quantity of Ca and Mg increased with time, and the exchange process reached 90% during 0-4 h and reached equilibrium after 24 h under 100 mg/L Na (the maximum Na concentration in Taihu sediment pore water). Our MINTEQ modeled result indicated that the exchanged quantity of Ca and Mg increased with the increasing Na concentration, with Ca being preferably exchanged over Mg at the same Na concentration. The MINTEQ model further predicted that, in the Taihu lake environment, the exchange adsorption would reach the equilibrium at the concentration of 6000 mg/L Na, with exchanged Ca2+ and Mg2+ accounting for 47% and 55% of the total exchangeable Ca and Mg in the sediment, respectively. Although current Na-induced exchange in the Taihu lake has been far from the equilibrium, the MINTEQ result confirmed the existence of this reaction and predicted the potential redistribution of base cations or Ca/Mg ratio in the lake sediment and water phase with further Na increase. Furthermore, our field observations not only confirmed the existence of Na-induced cation exchange in this lake environment but also were generally in agreement with our experimental and modeled results. The increased salinization-induced ion exchange would alter the re-distribution of base cations and the resulting potential ecosystem consequences should be given close attention in this large freshwater lake.

Investigation of water treatment sludge for the treatment of saline water: Batch studies

In this study, water treatment sludge was investigated through batch modes for the treatment of saline water to meet livestock drinking consents. The water quality was assessed using water quality index (WQI).The kinetic data was best described by the Pseudo - Second - Order model and the equilibrium isotherm by the Freundlich model. The maximum removal efficiency was 51.5 ± 0.65%, 22.6 ± 0.5% and 100% for Sulphates (SO₄ ^2-), Chloride (Cl^-), and Nitrates (NO₃ ^-), respectively. The maximum removal efficiency of sodium (Na) and nickel (Ni) was 100% each at 0.4g dose and that of manganese (Mn) was 87.5% at 1.2g dose. The effect of temperature revealed that the adsorption capacity for anions, decreased with increasing temperature, whereas for the cations the adsorption capacities increased with increasing temperature. The water treatment sludge reduced the total dissolved solids (TDS) and electrical conductivity (EC) from the initial values of 19600 mgL^-1 and 38900 μScm^-1 to 98 mgL^-1 and 1728 μScm^-1,respectively. The Water Quality Indices were 37.35 and 7.57, before and after treatment, respectively. Water treatment sludge can be used for the pre-treatment process before using conventional treatment technologies. Pilot scale investigations should be conducted before field trials.

Investigation of clay brick waste for the removal of copper, nickel and iron from aqueous solution: batch and fixed - bed column studies

The adsorption of copper, iron and nickel ions from an aqueous solution using Makoro granite clay brick waste through batch and fixed – bed column modes was investigated. The adsorbent was characterised using X-Ray Fluorescence, X-Ray Diffraction (XRD), Thermogravimetric Analysis, and Scanning Electron Microscopy (SEM). XRD results revealed crystalline peaks of Quartz (51.28 %) and mullite (23.40%) in fresh and loaded adsorbent with unnotable changes before and after adsorption. SEM images indicate the presence of micro pores and irregularly distributed surfaces. Batch kinetic maximum adsorption capacities for iron, copper, and nickel are 7.60, 6.70 and 6.20 mg g⁻¹ media respectively with 60 min as the optimum time. The maximum adsorption capacities at adsorbent dosage of 5 g L⁻¹ were 10.0, 7.60 and 7.20 mg L⁻¹ for iron, copper and nickel ions. The corresponding adsorption capabilities from the fixed-bed column reactor were 2.23, 2.22 and 0.74 mg g⁻¹ media respectively. The thermodynamics parameters of enthalpy change (ΔH) were 5.21, 9.32 and 5.22 kJ mol⁻¹ respectively for Copper, iron and nickel ions and the corresponding entropy change (ΔS) were -0.04, -0.05 and -0.03 kJmol⁻¹K⁻¹respectively and the process being non-spontaneous and exothermic. Thomas and Yoon-Nelson models yielded similar low coefficient of determination (R²) values (0.06 and 0.07) for copper and iron ions. Further investigations such as the use of real wastewater, competition of anions and further media characterisation and modifications are recommended.

Hierarchical porous structured zeolite composite for removal of ionic contaminants from waste streams and effective encapsulation of hazardous waste

A hierarchical structured composite made from clinoptilolite supported on date stones carbon is synthesized using two techniques. The composites are manufactured by fixing a natural zeolite (clinoptilolite) to the porous surface of date stones carbon or by direct hydrothermal synthesis on to the surface to provide a supported high surface area ion-exchange material for metal ion removal from aqueous streams. The fixing of the clinoptilolite is achieved using sucrose and citric acid as a binder. The composites and pure clinoptilolite were compared to test the efficacy for the removal of Sr²⁺ ions from an aqueous phase. The encapsulation of the Sr²⁺ using either vitrification or a geo-polymer addition was tested to ensure that the hazardous waste can be made safe for disposal. The hierarchical structured composites were shown to achieve a higher ion exchange capacity per gram of zeolite than the pure clinoptilolite (65mg/g for the pure natural clinoptilolite and 72mg/g for the pure synthesized clinoptilolite) with the synthesized composite (160mg/g) having higher capacity than the natural clinoptilolite composite (95mg/g). The rate at which the equilibria were established followed the same trend showing the composite structure facilitates diffusion to the ion-exchange sites in the zeolite.

2,4-Dinitrophenylhydrazine functionalized sodium dodecyl sulfate-coated magnetite nanoparticles for effective removal of Cd(II) and Ni(II) ions from water samples

2,4-Dinitrophenylhydrazine immobilized on sodium dodecyl sulfate (SDS)-coated magnetite and was used for removal of Cd(II) and Ni(II) ions from aqueous solution. The prepared product was characterized by X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The size of the nanoparticles according to SEM was obtained around 20-35 nm. In batch tests, the effects of pH, contact time, initial metal concentration, and temperature were studied. The kinetic and equilibrium data were modeled with recently developed models. The adsorption kinetics and isotherms were well fitted by the fractal-like pseudo-second-order model and Langmuir-Freundlich model, respectively. Maximum adsorption capacity by this adsorbent is 255.1 mg g(-1) for Cd(II) ion and 319.6 mg g(-1) for Ni(II) ion at pH 7.0 and 25 °C. The method was successfully applied to the removal of metal cations in real samples (tap water, river water, and petrochemical wastewater).