Analcime zeolite synthesis from the bottom ash of co-incinerated industrial hazardous and medical waste for tetracycline removal from wastewater

Abstract

Bottom ash (BA) produced from the centralized incineration of industrial hazardous waste and medical waste is a hazardous solid waste. Therefore, although challenging, it is necessary to develop recycling technologies that can convert BA into useful products. In this study, we developed a method for the preparation of analcime zeolite (ANA) via a BA acid leaching–melting–hydrothermal method. Unlike the existing method that involves using fly ash via a hydrothermal technology to synthesize mixed zeolites, such as NaPI zeolite (NaAl₆Si₁₀O₁₂·12H₂O), tobermorite (Ca₅Si₆(OH)₂O₁₆·4H₂O), sodalite (Na₄Al₃Si₃O₁₂Cl) and ANA (NaAlSi₂O₆·H₂O), the acid leaching–melting–hydrothermal method was used to synthesize pure ANA. ANA has application potential in the adsorption of wastewater pollutants. Herein, the synthesized ANA was used as an adsorbent to adsorb tetracycline (TC), ciprofloxacin (CIP), norfloxacin (NOR) and enrofloxacin (ENR) in water. Results of this study showed that ANA with a low impurity content could be synthesized using BA as the starting material. The adsorption capacities of ANA for TC, CIP, NOR and ENR were 134.2 mg g⁻¹, 64.3 mg g⁻¹, 56.5 mg g⁻¹ and 43.8 mg g⁻¹, respectively. The adsorption process of TC by ANA was studied. It was found that the optimal conditions were an adsorbent dose of 0.4 g L⁻¹, pH = 7, and a contact time of 300 min. The maximum adsorption capacity was 936.86 mg g⁻¹, which was much higher than the adsorption capacity of the existing zeolite for TC. The kinetic and isotherm fitting data showed that the adsorption of TC on ANA mainly involved monolayer chemical adsorption, and the process was more in line with the pseudo-second-order kinetic model and the Langmuir isotherm adsorption model. These results confirm that ANA is an efficient and economical TC adsorbent.