Bioscorodite: biological crystallization of scorodite for arsenic removal

The use of arsenic is banned for most applications, leading to its accumulation as arsenic trioxide and ferric arsenate sludge. The aim of this thesis was to develop a controlled process for biological crystallization of scorodite from metallurgical streams. In this thesis, the proof of principle, reactor selection and operational conditions of bioscorodite crystallization were studied. The results from this thesis resulted in the ARSENOTEQTM process, currently commercialized by Paques B.V. (Balk, The Netherlands).
The bioscorodite process in practice occurs in a continuous airlift reactor at pH < 2 and 70°C in a single step. Produced bioscorodite crystals resemble very well the scorodite mineral in their arsenic content and structural water content. The most stable crystals can be easily harvested by sedimentation from the bioreactor due to their larger sizes. Bioscorodite crystals were classified as non-hazardous material. This makes the bioscorodite sludge very suitable for long-term arsenic safe disposal.