Using hydrogel-biochar composites for enhanced cadmium removal from aqueous media

Abstract

Cadmium (Cd) is a common heavy metal and is often released into aquatic environment during mining activities and metallurgical processes. At high concentrations, Cd is highly toxic to most organisms and can be accumulated in organisms before entering human body through food chains. Many technologies have been developed to remediate Cd contamination, among which biochar is one of the most sustainable and promising. However, high pricing of biochar today is plaguing its large-scale applications. Therefore, in this study, inexpensive acrylamide was used to synthesize polyacrylamide hydrogel-biochar composites with the dosages of 1, 3 and 5% weight ratios of biochar. The swelling ratio significantly increased from 818% for untreated hydrogel to 1220, 1349 and 1506% for composites with increasing dosages of biochar, respectively. According to the isotherm experiment results, modeling simulations indicated that the maximum adsorption capacities (qmax) of the composites were 30.63, 59.21 and 63.58 mg/g for the three composites with increasing biochar dosages, respectively. In comparison, the untreated hydrogel had a much lower qmax of 24.72 mg/g. Besides the greater water swelling capacity, the significantly improved ability of hydrogel-biochar composites to entrap Cd from aqueous media was hypothetically attributed to the formation of ionic attraction fields around scattered biochar particles. It was recommended that 3% of biochar be the optimal dosage because further improvement became insignificant at higher dosages. The use of hydrogel-biochar composites for Cd contamination issues is a cost-effective approach.

Recent advances in biochar engineering for soil contaminated with complex chemical mixtures: Remediation strategies and future perspectives

“…The reason for the synergistic effect was linked to each single biochar particle scattered in the composite creating an ionic attraction field for attracting and retaining metallic ions such as Cd 2+. This ionic attraction field significantly extended the potential of each biochar particle to entrap ions within the cross-linked composite structure against large concentration gradient of ions (Li and Chen, 2018). The formation of many ionic attraction fields around the scattered biochar particles made it possible to overcome the ionic osmotic stress, the main factor regulating the sorption and release of ions in hydrogel materials (Wang et al, 2014).…”

“…The few adsorption studies conducted so far have shown promising results. For example, a biochar-hydrogel composite with 5% biochar was shown to significantly increase the swelling ratio of the hydrogel to 1506%, which is almost twice the size of the untreated hydrogel (818%), demonstrating great potential for the removal of Cd from soil (Li and Chen, 2018). Application of a biochar-digestate composite improved removal efficiency of Pb by nearly 100% when the composite dosage was applied at 1 g L −1 .…”

“…Moreover, the reusability (sustainably economical), lowcost associated with the purchase of chemicals needed for hydrogel synthesis, and biocompatibility (harmless to the physiology of biological organisms) of hydrogels add to the advantage of hydrogel (Table 2). The most common monomer for polymerizing hydrogel is acrylamide, whose market price can be as low as $1/kg (Li and Chen, 2018). Several studies of biochar-hydrogel composite ions were 1.43 and 2.04 mmol g −1 , respectively.…”

Equilibrium and Kinetic Studies for The Adsorptive Removal of Lead (II) Ions from Aqueous Solution Using Activated Plantain Peel Biochar

“…It assumes that adsorption takes place on homogenous site and ceases as sites become unavailable. The adsorption is thus monolayer without established interaction between the adsorbate [7,11,12]. Langmuir model is expressed with Equation 4. qe = Qm bCe 1 + bCe 4…”

A Review on Bamboo as an Adsorbent for Removal of Pollutants for Wastewater Treatment

“…Utilization of bamboo as a raw material for wastewater treatment has been increasing in recent years. Researchers have developed a variety of adsorbents derived from bamboo, including bamboo-activated carbon [9][10][11], bamboo biochar [12][13][14], and bamboo aerogel [15][16][17] among others.…”