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

Abstract

The presented work introduces the chemical modification of coal fly ash (FA) treated with NaOH and hexadecyltrimethylammonium bromide (HDTMABr) used as adsorbent for the removal of cadmium(II) ions and rhodamine B (RB) from aqueous solution. The FTIR spectrum shows the presence of organic and inorganic entities that are also seen on the XRD chart. The SEM analysis shows clearly the surface morphology and roughness of FA-HDTMABr. The effect of pH on adsorption equilibrium was studied. Maximum adsorption was found for pH values of 9. The Cd(II) ions and RB dye sorption is attributed to different mechanisms of the ion-exchange processes as well as to the adsorption. On the basis of reduced chi-square test (χ 2 /DoF) values obtained for both sorbates of the considered isotherms, the fitting degree follows the immediate sequence: Langmuir>Jovanović>Redlich-Peterson>Tóth>Freundl ich>generalized Langmiur-Freundlich>extended Jovanović>Halsey>Temkin>Dubinin-Radushkevich> Fumkin-Fowler-Guggenheim>Fowler-Guggenheim-Jovanović-Freundlich>Brunauer Emmett and Teller. The maximum monolayer adsorption capacity of the FA-HDTMABr was found to be 744 mg·g -1 and 666 mg·g -1 for Cd(II) and RB, respectively. The PFO, PSO, Elovich mass transfer, liquid film diffusion and intra-particle diffusion models were analysed. The PSO model (R 2 = 0.996) was slightly lower for Cd than those of the PFO model (R 2 <0.7), which is an indication that the PSO model was better than the PFO model. Purification water containing direct Cd and RB was made with 94% efficiency after 1 hour. We found that the chemical enhancement of FA from coal combustion by HDTMABr treatment yields an effective and economically feasible material for the treatment of basic dye and Cd(II) ions containing effluents.

Characterization of the Physical, Chemical, and Adsorption Properties of Coal-Fly-Ash–Hydroxyapatite Composites

“…The speciation of RB is strongly dependent on pH [105,106]. As shown in Figure 4, under acidic conditions, the cationic form predominates.…”

“…In an alkaline environment, RB assumes the closed uncharged form of lactone. Below pH 5, favorable adsorption is indicated as a result of electrostatic interactions between the RB cation and the deprotonated sorbent surfaces, as well as by ion exchange between the RB cation and the protonated sorbent surfaces [82,84,86,87,105,106]. At higher pH, the mechanism for the adsorption of the zwitterion RB particles involves complexing a lone nitrogen pair with a metal hydroxyl group on the adsorbent surface via hydrogen bonding through a water bridge [84].…”

Removal of Reactive Blue 21 (RB21) Phthalocyanine Dye from Aqueous Solution by Adsorption Process: a Review

“…Many dye removal methods have been tested and proven, including adsorption (physical method), which has emerged as one of the preferred dye removal techniques because of its exceptional ability to remove almost all types of dyes [18][19][20]. The adsorption means the deposition of a substance at the interface between two phases (gas-solid or liquid-solid).…”