Heterogeneous catalysis and complementary processes enable nutrient recovery and fertiliser production from biorefinery residues

Abstract Depletion of primary mineral nutrient resources, specifically phosphate rock, natural gas for nitrogen synthesis, and potash deposits, alongside accumulation of nutrient-bearing biomass processing residues create conditions in which circular biorefineries can reduce primary resource dependence. Biorefinery residues are structurally diverse materials whose agronomic potential is governed by nutrient speciation, phase distribution, and contaminant co-concentration rather than by total elemental content. This review examines heterogeneous catalysis and complementary interfacial recovery processes as the mechanistic platform connecting residue chemistry to nutrient recovery, fertiliser formulation, and circular biorefinery integration. Biorefinery residues are classified into three functional nutrient fractions (ammonium-rich aqueous streams, carbonaceous solid matrices, and inorganic mineral concentrates), each requiring a different combination of chemical transformation and separation. This review focuses on true heterogeneous catalytic reactions and distinguishes them from complementary non-catalytic operations, including adsorption, ion exchange, reactive crystallisation, and membrane separation. Thermochemical catalysis, electrocatalytic nitrogen transformation, surface-engineered sorbents, and membrane-integrated recovery are assessed according to their specific mechanisms and evidence bases. Heterogeneous catalysts and complementary functional materials, including metal oxides, zeolites, layered double hydroxides, supported metals, and functionalised biochars, are analysed according to active-site or interfacial chemistry, mechanism, and stability. Fertiliser product categories - mineral precipitates, organo-mineral composites, and slow-release formulations - are evaluated for release mechanism, agronomic performance, and soil-microbe interactions. Environmental, techno-economic, and regulatory dimensions are assessed to identify implementation barriers and research priorities. The explicit separation of catalytic transformations from sorption, ion exchange, crystallisation, and membrane operations sharpens the mechanistic contribution of the review.