New clues to the mechanism in controlling arsenic leaching from flash copper smelter flue dusts by using X-ray absorption spectroscopy

This paper characterizes the leaching of the toxic element (As) and other elements (Cu, Pb, Zn, Fe, Al, Cd, Mg, K, Ca, Mn, Co, Ni, Mo, Bi, and Sb) from the fresh and washed copper smelter flue dusts (FDs) over a wide pH range (3-12) based on the batch pH-static leaching experiment in combination with geochemical modeling. Furthermore, the leaching control mechanism of As was also explored on a microscale by using an X-ray absorption spectroscopy. Results revealed that the leached concentration of As showed a strong pH dependency, resulting in "L-shaped" leaching curves, similar to the leaching of Cu and Zn, whose leaching contents decreased dramatically with the increase of pH values. It should be noted that a partial of As was also released at the alkali conditions, especially from the washed FDs. Arsenic phases in the leachate were modeled by Visual MINTEQA 3.1 incorporated adsorption to Fe/Al hydroxides. The results were well in line with the actual leached content of As and showed that H3AsO3 is prevailing in the leachates at the pH range of 3-11, and AsO3- 4 is the dominant species in the alkali condition (pH = 12). Furthermore, the decreasing mineralogical composition of arsenolite and koritnigite in the washed FDs indicated that the above two arsenic-bearing phases primarily accounted for its release. According to the EXAFS analysis, ferric arsenates with a poorly crystalline scorodite structure in the raw FDs are important arsenic carriers, which could easily convert into crystalline scorodite at low pH. Furthermore, secondary Al hydroxides also have the potential to retain arsenate by forming a bidentate complex. Thus, As3+ species are the major resources for arsenic release from FDs and should be taken a crucial consideration when assessing its environmental risk. In contrast, arsenate was easily fixed by converting it into crystalline scorodite or adsorbing it onto Al hydroxides. This work may have important implications for the development of new ecofriendly technologies to reclaim valuable elements from the copper smelter flue dusts.