Geochemistry of aluminium and iron in mine soils from as Pontes, Galicia (NW Spain)

The geochemical processes influencing iron and aluminium mobilization and i mmobilization processes in mine soils are discussed. The study was carried out on 11 soils from the As Pontes mine dump, in the process of reclamation . The soils differ in age, spoils nature, reclamation tasks and type of veg etation, covering a wide range of physico-chemical conditions. Oxalate and pyrophosphate extractable Al and Fe (Alo, Alp, Fee, Fep), and dithionite ex tractable Fe (Fed) were analysed. These fractions were related to the solut ion Al and Fe forms and contents and to other soil properties (Eh, pH, sulf ides, organic matter, cation exchange capacity, and composition of the soil solution). Alo ranged between 2.2 and 111.2 cmolc kg(-1) 5 to 80% of this Alo was organic aluminium (Alp). Fed ranged between 8.5 and 215.6 cmolc kg( -1) 20 to 70% was poorly-criystalline iron (Feo). The solution concentratio ns of Al and Fe ranged between <0.1 and 319.2, and between <0.1 and 46.7 mg L-1, respectively. The results showed that the spoil nature (mostly carbon aceous clays and slates differing in sulfide content) and the reclamation t asks undertaken (topsoiling, liming with fly ash) determine the forms and c ontents of Al and Fe in the solid phase as well as in the soil solution and also its distribution between the solid and liquid phases.