Woods Charred at Low Temperatures and Their Modification for the Adsorption of Cr(VI) Ions from Aqueous Solution

Abstract

Despite being prepared at higher temperatures and involving greater energy consumption, activated carbons always show a smaller capacity and affinity towards the adsorption of Cr(VI) ions. After a brief review regarding Cr(VI) ion contamination and treatment, the preparation of a novel biosorbent from pyrolyzed wood char for Cr(VI) ion adsorption is described. Pyrolysis was conducted at temperatures within the range 200-350 ºC, thereby helping to protect beneficial functional groups, saving energy and hence reducing costs.The influence of pH, concentration, adsorbent dosage, ionic strength and equilibration time on Cr(VI) ion adsorption by this biosorbent was investigated. It was shown that the char obtained at 200 ºC possessed the highest Cr(VI) ion retention capacity (31.96 mg/g) but required the longest equilibration time (> 47 d). Coating the char with nano-scale iron oxide greatly improved its adsorption affinity towards Cr(VI) ions, with a higher adsorption affinity (Henry's law K d = 2.988 ᐉ/mg) and an enhanced Cr(VI) ion adsorption capacity (53.45 mg/g) being accomplished within a much shorter equilibration time (24 h). Spectroscopic studies confirmed that complexation of Cr(VI) ions occurred via surface hydroxy groups. The methods proposed for preparing and modifying wood char are likely to be applicable in industrial wastewater treatment.

Effect of porous zinc–biochar nanocomposites on Cr(vi) adsorption from aqueous solution

“…As seen, the prepared zinc-biochar nanocomposites maintained much higher Cr(VI) removal performance than many other adsorbent materials reported in the literature. [41][42][43][44]…”

A novel graphene oxide coated biochar composite: synthesis, characterization and application for Cr(vi) removal

“…An adsorption kinetic study was carried out with an initial Cr(VI) concentration of 100 mg L À1 at 30 C and pH 2.0 to determine the minimum time required for equilibrium adsorption. The concentrations of Cr(VI) were measured at different time intervals from 15 to 2880 min (15,30,60,120,180,360,480, 600, 720, 1080, 1440, 2160 and 2880 min). To evaluate the maximum adsorption capacity and thermodynamic properties, adsorption isotherms of Cr(VI) on WHB-GO were obtained at pH 2.0 at 30 C, 40 C and 50 C, respectively.…”

“…Previous studies have been reported that several methods, such as acid and alkali modication, oxidation, and chemical gra, have been used to improve their functional group contents and enhance their adsorption performance. 15,16 However, these previous modied biochar have some disadvantages: such as non-ideal adsorption capacity, occurrence of secondary pollution during production, low reutilization rate and high price. 17 Thus, it is necessary to develop an efficient, environmentally friendly and low-cost adsorbent to remove Cr(VI) from aqueous solution.…”