Arsenic Removal From Flue Gas Condensate with Ferrihydrite Precipitation.

Sammanfattning: At the Idbäcken combined heat and power (CHP) plant waste wood is combusted. The flue gas from the combustion is condensed and heavy metals and other toxic species ends up in the condensate water. Since the condensate water in this way contains many toxic substances it needs to be treated before it is sent to the recipient Kilaån (the Baltic Sea). Arsenic (As) is one substance that needs to be removed, and this thesis aims to find the optimal conditions for As removal by using precipitation with iron(III) chloride (FeCl3). When FeCl3 comes in contact with water it forms ferrihydrite, an efficient sorbent due to its high specific area. The adsorption of As to ferrihydrite is dependent on different variables; pH, Fe(III) dosage, competitive ions et cetera. Lab-scale experiments have shown that a pH value between 3 and 8 is required for efficient As removal. Concerning the Fe(III) dosage further experiments are needed in order to tell what dosage that is the optimal in this case. Further, the removal of metals has also been studied. A comparison between two chemicals (TMT 15 and MP 7) used for metal removal has been made, which showed that TMT 15 is to prefer for metal removal. Also, it was found that efficient removal of metals require pH > 5, preferably in the slightly alkaline pH range.