Chemical speciation of phosphorus in farmland soils and soil aggregates around mining areas

•Fe/Al-P dominated in acidic soils, while some Ca-P occurred in alkaline soils.•Available P, total P, and their ratio increased substantially in the soil colloids.•Fe-P increased while Ca-P decreased in the colloids compared with macroaggregates.•HMs seemed no significant effects on P speciation in the polluted farmland soils.•Al fractions played important roles in P immobilization by pedogenic Fe/Al oxides.