Adsorption of CdII by synthetic zeolite under multi-factor using response surface methodology

Bolivian natural zeolite as a low-cost adsorbent for the adsorption of cadmium: Isotherms and kinetics

Population growth in recent years has led to increased wastewater production and pollution of water resources. This situation also heavily affects Bolivia, so wastewater treatment methods and materials suitable for Bolivian society should be explored. This study investigated the natural Bolivian Zeolite (BZ) and its NaCl-modified structure (NaBZ) as adsorbents for cadmium removal from water. The natural BZ and the modified form NaBZ were investigated by different physicochemical characterization techniques. Furthermore, XPS and FT-IR techniques were used to investigate the adsorption mechanisms. The cadmium adsorption on BZ and NaBZ was analyzed using various mathematical models, and the Langmuir model provided a better description of the experimental adsorption data with cadmium adsorption capacities of 20.2 and 25.6 mg/g for BZ and NaBZ, respectively. The adsorption followed the pseudo-second order kinetics. The effect of different parameters, such as initial cadmium concentration and pH on the adsorption was studied. In addition, the results of the regeneration test indicated that both BZ and NaBZ can be regenerated by using hydrochloric acid (HCl). Finally, the adsorption experiment of BZ and NaBZ on a real water sample (brine from Salar de Uyuni salt flat) containing a mixture of different heavy metals was carried out. The results obtained in this study demonstrate the effectiveness of natural BZ and modified NaBZ in the removal of heavy metals from wastewater.

Structural analysis of lignite-derived humic acid and its microscopic interactions with heavy metal ions in aqueous solution

Understanding heavy metal environmental behavior with humic acid (HA) is critical. There is currently a lack of information on the control of its structure organization on its reactivity to metals. The difference in HA structures under non-homogeneous conditions is critical for revealing its micro-interaction with heavy metals. The heterogeneity of HA was reduced using the fractionation method in this study, the chemical properties of HA fractions were analyzed using py-GC/MS, and the structural units of HA were proposed. Pb2+ was used as a probe to investigate the difference in the adsorption capacity of HA fractions. The microscopic interaction of structures with heavy metal was investigated and validated by structural units. The results show that as molecular weight increased, the oxygen content and the number of aliphatic chains decreased, but the opposite was true for aromatic and heterocyclic rings. The adsorption capacity for Pb2+ was as follows: HA-1 > HA-2 > HA-3. According to the linear analysis of the influencing factors of maximum adsorption capacity and possibility factors, the adsorption capacity was positively correlated with the contents of acid groups, carboxyl groups, phenolic hydroxyl groups, and the number of aliphatic chains. The phenolic hydroxyl group and the aliphatic-chain structure have the greatest impact. Therefore, structural differences and the number of active sites play an important role in adsorption. The binding energy of HA structural units to Pb2+ was calculated. It was found that the chain structure is easier to bind to heavy metals than aromatic rings, and the affinity of-COOH to Pb2+ is greater than that of -OH. These findings can help improve the adsorbent design.