To "nbucska", As I am not realy sure what Maniam is trying to achieve I can't give you a full answer, but there is merit in your question. Arsenic is soluable if and when it exceeds the iron (Fe) chemically by 4:1, thus extra iron will precititate As. However, ferric iron is insoluable at any pH 4 - 12 thus any surplus will precipitate, and not be available to react with the cyanide, bi-valent iron would react. A further problem is that ferric chloride is very, very corrosive. Stainless Steel lasts mere minutes, only plastic, or titanium alloys are safe. Thus Ferric Chloride is only used if the treated water is not being recycled, with Ferric sulphate being prefered.
However, one needs a better insight of what Maniam aims to do. Even as engineers we need to stay within our experience. Though the only way to learn is by asking questions, so its a pleasure to answer those I can
Regards. broadfam@ntl.sympatico.ca