Adsorption kinetics and equilibrium of Ni2+, Cu2+, Co2+, and Ag+ on geopolymers derived from ashes: application to treat effluents from the E-Coat printing process

Geopolymers were obtained from ashes through an alternative geopolymerization process and applied to remove Ni²⁺, Cu²⁺, Co²⁺, and Ag⁺ from synthetic aqueous media and real effluents. The study in synthetic solutions revealed that pseudo-second-order and general order models were the best to fit the kinetic curves. To represent the equilibrium curves, Langmuir and Freundlich were the most adequate. The geopolymer derived from bottom ash (GHA) was superior to adsorb Cu⁺², Co⁺², and Ag⁺¹ than the geopolymer derived from fly ash (GFA). GHA reached adsorption capacities of 279.5, 288.2, and 462.8 mg g^-1 for Co⁺², Cu⁺², and Ag⁺¹, respectively. Otherwise, GFA was the best for Ni⁺² removal, with an efficiency of 95% in low concentrations. In treating real effluents of the E-coat printing process, both GHA and GFA were efficient, with the removal of higher than 85% for all the metals. In brief, it can be stated that GFA and GHA prepared are promising materials to remove metals from aqueous media (synthetic and real), presenting fast adsorption kinetics, high adsorption capacity, and high metal removal percentage.

Synthesis of geopolymers from fly and bottom ashes of a thermoelectrical power plant for metallic ions adsorption

A series of geopolymers were synthesized from fly and bottom ashes of a thermoelectrical power plant located in the Brazilian southern, aiming to add value for these wastes. The geopolymers were prepared in conventional and ultrasound-assisted ways and used to uptake Ag⁺, Co²⁺, Cu²⁺, and Ni²⁺ from aqueous solutions. All materials were characterized by infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and N₂ adsorption isotherms (BET and BJH methods). The results revealed that the geopolymers obtained from the conventional method presented slightly higher values of surface area and total pore volume. However, in some cases, the adsorption potential was better for the ultrasound synthesized materials. The geopolymers prepared from both methods presented good adsorption performance concerning Ag⁺ and Cu²⁺, Co²⁺ and Ni²⁺. The removal percentages were higher than 90%. In addition, the adsorption capacities were within the literature range. These findings show that the ultrasound technique is not essential to improve the geopolymers production process compared to the conventional process, which generated material with better performance for heavy metals adsorption. Besides, it was possible to aggregate value for fly and bottom ashes, generating promising adsorbent materials.

Development of CO2 activated biochar from solid wastes of a beer industry and its application for methylene blue adsorption

An alternative activated biochar was developed from barley malt bagasse (BMB) through pyrolysis followed by CO₂ activation. The materials BMB, biochar and activated biochar (CO₂-biochar) were characterized and tested as adsorbents for the removal of methylene blue (MB) from aqueous solutions. Adsorption kinetics, equilibrium and thermodynamics were studied. It was found that BMB and biochar presented surface area values lower than 1 m² g^-1, while CO₂-biochar was a typical mesoporous material with surface area around 80 m² g^-1. As consequence, the adsorption potential for methylene blue was in the following order CO₂-biochar ≫ biochar > BMB. Adsorption kinetics of MB on CO₂-biochar followed the pseudo-second order model. Langmuir presented the best fit with the equilibrium adsorption isotherms. The maximum adsorption capacity was 161 mg g^-1. MB adsorption on CO₂-biochar was spontaneous, favorable and exothermic. Pyrolysis followed by CO₂ activation was a suitable route to produce an alternative mesoporous adsorbent from barley malt bagasse.