Development of Mg/La-layered double hydroxide nanocomposites and application of recovered phosphorus from modelled biogas slurry

Presently, a large amount of agriculture-produced sewage generally contains excessive phosphorus discharge and water eutrophication. However, it is difficult to recover phosphorus from biogas slurry. Among phosphorus recovery technologies, adsorption technology has more advantages, including its simple operation, low cost, high selectivity, and environmental friendliness. Furthermore, it is a type of technology with “mature” prospect. Highly efficient and cost-effective adsorbents are crucial to control eutrophication and recover phosphorus from biogas slurry. This study reports the synthesis of three nanocomposites of Mg/La-layered double hydroxide, Mg/Al-LDH, and Mg/Fe-layered double hydroxide. The effects of Mg/La-LDH materials synthesised with different La concentrations on phosphorus recovery from biogas slurry are discussed. It was found that Mg/La-LDH with low La concentration has better phosphorus adsorption than Mg/La-LDH with high La concentration. The maximum phosphorus adsorption capacities of 284.11 and 378.80 mg g −1 were achieved by La 0.001 and La 0.1 (Mg/La at molar ratios of 0.05/0.001 and 1.0/0.1, respectively) nanocomposites at pH 10.60–11.50. Their recovery rates in phosphorus solution reached 99.58% and 99.15%, respectively. Compared with that of other phosphorus adsorbents, the recovery efficiency of phosphorus from the modelled biogas slurry was significantly improved. Interlayer anion exchange between PO 4 3− and CO 3 2− of the hydrotalcite layer and surface complexation of stable complexes (LaPO 4 ) and Mg 3 (PO 4 ) 2 were the predominant adsorption mechanisms under the studied solution. The special flower-like cluster structure of the layered double hydroxide promotes the formation of ionic bonds between PO 4 3− and Mg 2+ /La 3+ , which is crucial for phosphorus adsorption. La 0.001 and La 0.1 materials can potentially enhance phosphorus recovery in biogas slurry.