Lead blast furnace (LBF), one of the processes used in non-ferrous metallurgy, generates huge amounts of primary smelting slags which are often directly landfilled. The slags sampled from the industrial basin of Nord-Pas-de-Calais (northern France) still contain significant quantities of lead and zinc and are exposed to weathering conditions at their disposal site. Thus, the aim of this study was to investigate metal leachability when LBF slags come into contact with ultrapure water, sterile growth media or growth media inoculated with a heterotrophic bacterium (Pseudomonas aeruginosa). The changes in the surface morphology of slag prior and after the alteration experiments as well as the formation of secondary mineral phases has been monitored by Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray Analysis (EDX). P. aeruginosa was shown to play a significant role in LBF slags weathering by enhancing the leaching and solubility of toxic elements (Zn and Pb) present in LBF slags. Sorption of Zn and Pb onto bacterial cells and complexation of these toxic metals by siderophores is expected to dramatically enhance the solubility, and therefore the mobility of these metals. Leached out elements were further complexed either with phosphate present in the growth medium or with carbonate which led to the formation of secondary Zn or Pb precipitates.•Pseudomonas aeruginosa growth alone is capable to enhance LBF alteration.•P. aeruginosa enhances toxic elements (i.e. Pb, Zn) solubility.•Medium composition strongly influences major and trace elements solubility.•Carbonate and phosphate is controlling major and minor elements precipitation.•Bulk liquid modeling corroborates the results of secondary precipitates analysis.