Highly Efficient Adsorption of Cd(II) onto Carboxylated Camelthorn Biomass: Applicability of Three-Parameter Isotherm Models, Kinetics, and Mechanism

Abstract

A series of malonic acid treated camelthorn (MATC) sorbents were produced via the reaction of camelthorn biomass with malonic acid, and factors affecting the extent of modification were investigated, including malonic acid concentration, dehydration time and temperature. The optimum sorbent, by carboxylic acid content, was subsequently characterised for surface charge behaviour (pHPZC), surface chemical functionalities (FTIR), morphological structure (SEM), and available surface area. The sorbent was subsequently utilised for adsorption of Cd(II) ions from aqueous media, and parameters influencing adsorption at 30 °C, such as sorbent dose, initial solution pH, exposure time, metal concentration, were investigated. Isothermal analyses were performed using eight models, including two and three parameter equations, with appropriateness of fit assessed via non-linear regression analysis. The adsorption data indicated that the Langmuir model gives the most appropriate fit to experimental curves, with the models ordered as Langmuir > Hill > Toth > Sips > Jossens > Khan > Redlich-Peterson > Freundlich. The highest uptake (qmax) of 582.6 mg g−1 was determined at pH 6. The Freundlich constants, KF and n, at 30 °C were found to be 24.94 mg g−1 and 2.33, respectively. The value of n (2.33), being in the range 0–10, indicates that adsorption of Cd(II) ions onto malonic acid treated camelthorn biomass is favourable. Evaluation of a series of kinetic models, allowed elucidation of the adsorption mechanism, as a pseudo-second order model gave the most appropriate fit, indicating that chemisorption processes are involved. Cd(II) ions adsorption onto MATC is enhanced by a higher level of active surface sites but was show to be independent of surface area. The work presented here indicates that this sorbent offers effective adsorption potential for Cd(II) ions from water, with potential in wastewater processing.

Inversion of loading‐implicit adsorption isotherms by means of the Lambert W function

“…It should also be noted that the Redlich–Peterson isotherm was mistakenly referred to as the Jossens isotherm in some papers published in the 1980s 46,47 . This misattribution can still be found in some recent studies 48‐52 . The Jossens isotherm, defined by Eqn (5), has been used by several researchers to correlate liquid phase 5‐8,38‐45,53‐58 and gas phase 59‐61 adsorption data since the 1980s.…”

“…46,47 This misattribution can still be found in some recent studies. [48][49][50][51][52] The Jossens isotherm, defined by Eqn ( 5), has been used by several researchers to correlate liquid phase [5][6][7][8][38][39][40][41][42][43][44][45][53][54][55][56][57][58] and gas phase [59][60][61] adsorption data since the 1980s. Least-squares fitting methods were used to estimate the three parameters of the Jossens isotherm.…”

The Sips isotherm equation: Often used and sometimes misused

“…To illustrate this point, Fig. 4 shows the fits of the Sips, Langmuir, and Freundlich equations to a set of cadmium isotherm data taken from the work of Hashem et al [49] As can be seen in Fig. 4, the measured cadmium isotherm manifests a type I curve shape without an apparent plateau.…”

Adsorption and removal studies of cadmium ion onto sulphonic/phosphonic acid functionalization resins

“…[11] There are several techniques such as adsorption, [12] ion exchange, membrane, filtration, electro-sorption, reverse osmosis, ultrafiltration, and photocatalysis applied for the removal of cadmium and other heavy metal ions from the water system. [13][14][15][16][17] Among these technologies, the ion exchange process is one of the most efficient methods for thorough cadmium removal from different aqueous solutions because it has advantages, such as being effective at a low metal concentration, simple operation, low cost, and easy regeneration of resins. [18,19] Ion exchange resins (beads) are solid and insolubilized high-molecular-weight polyelectrolytes that can exchange their mobile ions for ions of the same charge from the surrounding medium according to an electric charge balance.…”