Comparison of adsorption of Cd(II) and Pb(II) ions on pure and chemically modified fly ashes

Abstract

The study investigates chemical modifications of coal fly ash (FA) treated with HCl or NH4HCO3 or NaOH or Na2edta, based on the research conducted to examine the behaviour of Cd(II) and Pb(II) ions adsorbed from water solution on treated fly ash. In laboratory tests, the equilibrium and kinetics were examined applying various temperatures (293 - 333 K) and pH (2 - 11) values. The maximum Cd(II) and Pb(II) ions adsorption capacity obtained at 293 K, pH 9 and mixing time 2 h from the Langmuir model can be grouped in the following order: FA-NaOH > FA-NH4HCO3 > FA > FA-Na2edta > FA-HCl. The morphology of fly ash grains was examined via small-angle X-ray scattering (SAXS) and images of scanning electron microscope (SEM). The adsorption kinetics data were well fitted by a pseudo-second-order rate model but showed a very poor fit for the pseudofirst order model. The intra-particle model also revealed that there are two separate stages in the sorption process, i.e. the external diffusion and the inter-particle diffusion. Thermodynamics parameters such as free energy, enthalpy and entropy were also determined. A laboratory test demonstrated that the modified coal fly ash worked well for the Cd(II) and Pb(II) ion uptake from polluted waters.

Waste Plant Material as a Potential Adsorbent of a Selected Azo Dye

“…(2) and (3) are frequently used (Ho and Wang, 2004;Ho, 2006;Sočo and Kalembkiewicz, 2016). When the adsorption mechanism is mainly physical, the kinetics is usually described with Eq.…”

Novel Application of Mineral By-Products Obtained from the Combustion of Bituminous Coal–Fly Ash in Chemical Engineering

“…A combined process of precipitation (Cr(OH) 3 , Cd(OH) 2 ) and adsorption (Cr(OH) 4 − ) at pH > 9 was observed (Figure 6a,b). The order of affinity based on the amount of sorbate removal is as follows, with a hydrated ion radius: Cr(III) (4.13 Å) > Cd(II) (4.26 Å) > CV (above 40 Å) [37]. It was found that the sorption process predominates between positively charged CV molecules and the negatively charged silanol group.…”

“…Then, the mixtures were subjected to agitation at pH 9.0 for 1.5 h (see Section 3.4.1). The method was described according to the work in [37].…”

Immobilizing and Removal of Cadmium and Rhodamine B from an Aqueous System by Converting Solid Waste from Poland; Studies of Equilibrium and Kinetic Sorption

“…The process of precipitation (Cd(OH) 2 ) and adsorption (CdOH + ) at pH 6-9 was observed. Moreover, at pH>9 it was also the combined process of precipitation (Cd(OH) 2 ) and adsorption (Cd(OH) 3ˉ) [19]. When the pH is higher than 7 the aggregation of RB decreases because excessive OHˉ competes with COOˉ in binding with -N + and the lactone form of RB is formed (Fig.…”

“…The selectivity sequence of metal and dye is generally explained on the basis of the properties of ion size, such as the smallest hydrated ionic radii (4.26Å) and RB cation weight. It is possible that the Cd(II) ions with fewer weakly bonded water molecules tend to move faster to potential adsorption sites on FA-HDTMABr, compared to the RB cations with higher ionic radii [19]. Langmuir isotherm is often used to describe adsorption of solutes from liquid solutions and the model assumes monolayer adsorption onto a homogeneous surface with a finite number of identical sites [27,28].…”