Abstract
Lignocellulose (LCE) was ultrasonically treated and intercalated into magnesium aluminum silicate (MOT) clay to prepare a nano-lignocellulose magnesium aluminum silicate polymer gel (nano-LCE-MOT) for the removal of Zn (II) from aqueous solution. The product was characterised using nitrogen adsorption/desorption isotherm measurements, Fourier-transform infrared spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The conditions for the adsorption of Zn (II) on nano-LCE-MOT were screened, and adsorption kinetics and isotherm model analysis were carried out to explore the adsorption mechanism and achieve the optimal adsorption of Zn (II). Optimal adsorption was achieved at an initial Zn (II) concentration of 800 mg/L at 60 °C in 160 min at a pH of 4.52. The adsorption kinetics were explored using a pseudo-second-order model, with the isotherm adsorption equilibrium found to conform to the Langmuir model. The maximum adsorption capacity of the nano-LCE-MOT polymer gel toward Zn (II) is 513.48 mg/g. The materials with adsorbed Zn (II) were desorbed using different media, with HCl found to be the most ideal medium to desorb Zn (II). The optimal desorption of Zn (II) was achieved in 0.08 mol/L HCl solution at 65 °C in 60 min. Under these conditions, Zn (II) was almost completely desorbed from the adsorbents, with the adsorption effect after cycling being slightly different from that of the initial adsorption.
Highlights
Heavy metals that are released into the environment tend to persist indefinitely, circulate and eventually accumulate throughout the food chain, posing a serious threat to the environment, animals and humans [1,2,3]
From the results shown in attributed to -OH bending (3366 cm−1), the –OH stretching vibration of -COOH (1462 cm−1) and the -C-O-C- stretching vibration of cellulose and hemicellulose (1050 cm−1) [41], while after nanosizing treatment, the absorption peaks were shifted to 3360, 1474 and 1037 cm−1, respectively, and a new peak attributed to -C=O appeared at 1622 cm−1 [42], indicating that the active groups of lignocellulose were exposed after the nanosizing treatment
As shown in the data, after adsorption, these peaks shifted to lower wavenumber values of 3374 and 3349 cm−1 respectively, indicating that the -O-H groups of nano-LCE-MOT and LCE-MOT participated in the adsorption process, which in turn demonstrates the involvement of oxygen in the chemisorption of Zn (II) in the subsequent complexation process
Summary
Heavy metals that are released into the environment tend to persist indefinitely, circulate and eventually accumulate throughout the food chain, posing a serious threat to the environment, animals and humans [1,2,3]. In the presence of zinc sulphides, carbonates, silicates, and oxides are formed in Nature. Zn (II) dust is irritating to the eyes and when orally ingested affects the gastrointestinal tract. With this in mind, there are many treatment technologies available to purify water and wastewater contaminated with such heavy metals. The most common methods for removing metal ions from wastewater include chemical precipitation [5,6], extraction [7], redox [8], dialysis [9], electrodialysis [10], electrolytic extraction [11], reverse osmosis [12,13], ion exchange [14,15], adsorption [16,17,18,19,20], ion flotation [21], stripping [22], coagulation flocculation [23], precipitation [24,25] and chelation [26]. Selective adsorption can be carried out using biomass materials, such as inorganic clay, activated carbon or polymer resins
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