Arsenic attenuation in tailings at a former Cu-W-As mine, SW Finland

► Arsenic attenuation occurred in the vadose zone of tailings at the Ylöjärvi Cu-W-As mine. ► Iron(III) (oxy)hydroxides and Fe(III) arsenates contributed to As attenuation. ► Variations in chemical composition and crystallinity may influence As stability. ► Geochemical conditions favored the stability of Fe(III) (oxy)hydroxides over Fe(III) arsenates.