ResinTech SIR-400 is a free base form macroporous heavy metal selective weakly basic anion resin. SIR-400 has unique thiouronium functionality and is able to remove mercury and other heavy metals to very low levels (when present as divalent cations). SIR-400 is also quite selective for noble metal cations. SIR-400 is intended for mercury removal and for removal/recovery of various precious metals, when present in cationic form. SIR-400 is supplied in the free base form.