Synthesis of steel slag ceramsite modified with lanthanum-iron-zinc composite oxide and its effect on phosphorus removal and algal inhibition

Phosphorus serves as a vital element for algae growth in aquatic bodies and is a significant factor contributing to water eutrophication. This study aims to explore the phosphorus removal and algal inhibition capabilities of modified steel slag ceramsite (LFZSC) prepared through calcination using lanthanum oxide (La₂O₃) and iron-doped zinc oxide (Fe-ZnO) as modifiers. The morphology and structure of LFZSC were characterised and analysed using scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) surface area analysis. With <i>Chlorella vulgaris</i> as the test organism, the inhibitory effects of LFZSC on its growth under various conditions were investigated through algae cell counting, chlorophyll-a measurement, photosynthetic activity assessment, polymerase chain reaction (PCR) analysis and electron paramagnetic resonance (EPR) spectroscopy. The results showed that the modified steel slag ceramsite had larger pores, a loose and rough surface with more uneven folds. The phosphorus adsorption capacity of 0.098 mg/g by LFZSC matched the quasi-secondary kinetic model. When LFZSC was dosed at 20 g/L, the removal of phosphorus and algae was 93.57% and 47.66% in a 100 mL system with an initial phosphorus concentration of 1.0 mg/L and an initial algal concentration of 3.4 × 10⁶ cells/mL. On the 5 d following LFZSC treatment, the inhibition rate of photosynthetic activity was 67.68% and the inhibition rate of chlorophyll-a was 76.13%. In addition to seriously harming the chloroplast gene <i>psb</i>A, the hydroxyl radicals produced by LFZSC also poisoned algal cells. This study provides novel insights into the removal of phosphorus from water and the sustained inhibition of algae growth.