Chelating polymers with nitrogen donor atoms: Their unique properties in relation to heavy metals sorption and ligand exchange.

摘要

This dissertation studies two specific areas of separation processes: (1) heavy metals sorption and, (2) removal of hydrophilic organic solutes through polymeric ligand exchange.; Primary findings of the study can be summarized as follows: (1) Chelating exchangers with nitrogen donor atoms showed high affinity toward dissolved metal ions even under highly acidic conditions i.e., at pH {dollar}leq{dollar} 3.0. (2) It was observed that the metal-ion affinity toward these chelating polymers can be easily enhanced with an increase in electrolyte concentration. (3) This study identified the prevailing metal-ion-binding mechanism, which can quantitatively explain the unusual sorption behaviors of this new class of chelating polymers as described in (1) and (2). "Molar exchange" rather than more commonly encountered "ion exchange" was found to be the primary mechanism through which dissolved heavy metals attach themselves onto the sorption sites of these chelating polymers. (4) In general, these chelating polymers showed high affinities toward relatively soft Lewis acid-type heavy metal ions (e.g., Cu{dollar}sp{lcub}2+{rcub}{dollar}, Ni{dollar}sp{lcub}2+{rcub}{dollar}) compared to hard but non-toxic competing cations, namely, Al{dollar}sp{lcub}3+{rcub}{dollar}, Fe{dollar}sp{lcub}3+{rcub}{dollar} and Ca{dollar}sp{lcub}2+{rcub}{dollar}. (5) Because of somewhat unique metal-ion-binding properties, these chelating polymers with nitrogen donor atoms were able to remove dissolved heavy metals in the presence of strong ligands, namely, nitrilotriacetate (NTA). (6) Contrary to other conventional chelating exchangers, these chelating exchangers with nitrogen donor atoms can be efficiently regenerated with ammonia.; Tailored sorbents, namely, transition-metal-loaded chelating exchangers with nitrogen donor atoms, showed high affinity toward anionic organic solutes over competing sulfate and chloride anions. Anion exchange accompanied by Lewis acid-base interaction (or metal-ligand interaction) is the underlying reason for such high selectivities toward anionic organic ligands (i.e., oxalate and phthalate) and the sorption may be viewed as a ligand-exchange process between the solid polymer phase and the aqueous phase. Also, this polymeric ligand-exchange process appears to hold a great promise for selective removals of other inorganic and organic ligand (anions) such as arsenates, selenites, cyanides and chlorinated aliphatic and aromatic acids.; Polymeric ligand exchangers (PLE) are likely to be very effective for selective removals of natural organic matters i.e., humates and fulvates. In this regard, the PLEs have a specific advantage over activated carbons because unlike activated carbons, they are amenable to in-situ regeneration. (Abstract shortened by UMI.)