Mechanism of Pb(II) adsorption on a sodium alginate composite based on Diatomite/Crab shell biochar

Industrial wastewater containing heavy metal ions has become an urgent problem to be solved due to its environmental persistence and bioaccumulation. In this study, powdered adsorbent (DE/CBC) and spherical adsorbent (SA@DE/CBC) were prepared from natural diatomite (DE), crab shell biochar (CBC) and sodium alginate (SA) as raw materials, and were used to adsorb Pb(II) from wastewater. The adsorption isotherm fitting showed that the experimental process of DE/CBC and SA@DE/CBC conformed to the Langmuir model, and the maximum adsorption capacity of the monolayer reached 1155 mg/g and 365 mg/g, respectively. The pseudo-first-order kinetic model showed better fitting for the two adsorbents, and the diffusion rate was controlled by multiple steps. Compared with most traditional composite adsorbents, DE/CBC and SA@DE/CBC can achieve 98 % and 93 % adsorption rates at relatively high Pb(II) concentrations, and maintain 83 % and 84 % high adsorption capacity after 10 adsorption–desorption cycles, demonstrating superior Pb(II) adsorption performance and excellent structural stability. The spherical morphology not only effectively solves the problems of adsorbent recovery and secondary pollution prevention and control, but also plays a role in protecting the structure and active sites of powdery materials, making it more durable and practical. Collectively, the developed composite not only enables high-value-added utilization of biowaste but also demonstrates cost-effectiveness and excellent reusability, providing a sustainable remediation strategy for lead-contaminated water systems.