The contamination of soils with copper in the vicinity of Aurubis copper smelter and refinery in Bulgaria is a problem that needs further studies. Water soluble concentrations of Cu, Pb, Mn and Fe exceeded the maximum permissible concentrations for domestic water quality. Principal component analysis (PCA) revealed that Cu, Pb, Mn, Cd and Co are of anthropogenic origin, Ni, Cr and Fe are both of anthropogenic and pedogenic, while Zn has pedogenic sources in the studied soils. Biochar (BC) added at 1, 5, 10, 20% w/w led to a total decrease of Cu and Pb in solution and increased dissolved organic carbon (DOC) and pH. Ion speciation modelling (Visual Minteq) for Cu, Pb, Cd, Zn, Cr, etc. in the non-treated variants and those with pH 4.7-5 revealed that the majority of species were represented by the free Men+ ions, while with increasing incubation time and BC rates, heavy metal species, were represented by organic fulvic acid-metal complexes, such as bidentate (FA(2)M) and M-FA gel fraction species, e.g. FAM + 2G; FA-Cr + 3G. The total Cu concentration decreased by similar to 70%, while Cu2+ species decreased to similar to 3,7% of the total concentration at the 4th month of incubation for some soils. Biochar had a positive effect both on Cu, Pb and other metals total solubility, as well as on metal speciation in favour of increasing metal-organic complexes in soil solution, which are less mobile and bioavailable.