Study On The Effect Of Polysaccharide And Protein Modulating The Biomineralization Of Iron Minerals

Iron minerals are the main constituent of waters, soils, sediments and rocks in nature. The changes of iron minerals will take a great impact on the geochemical properties of the environment in which they exist, such as the fertilities of soils, degradation of organic matter, adsorption and release of the heavy metal elements and so on. Owing to their stable properties, high surface areas and high reactivity, iron minerals have good performance as adsorbent and so have prominent effects on the transportation, transformation, and precipitation for a large number of cations, anions, metal ions, and organic chelates in subsurface environment. So they have many advantages such as good and inmitable compatibility as materials for the treatment of polluted environment. Meanwhile, the formation of iron minerals is closely related to the mineralization effect of microbes. It is also a hot spot using organic matrix as template to synthesize nanoscale iron oxides in the field of materials research. For these reasons, the focus of this article is to study how biological polysaccharide and protein to modulate the mineralization and crystallization process of Fe(OH)₃ gel. The results will have an important theoretical meaning.In this paper, the simulative biominealization experiments were studied which performed under normal temperature and medium pH. Dextran, Chitosan, Carboxymethylchitosan and gelatin were used respectively as organic matrices in those mineralization systems. The purpose was to study the effects of biological polysaccharide and protein modulating the mineralization behavior of Fe(OH)₃ gel and its mechanism. The results showed that biological polysaccharide and protein could control the crystal structure, morphology, properties and growth modes of the minerals by selecting the mechanism of nucleation and transformation. Different polysaccharide and protein had different active functional groups acted as nucleation sites, which can attract Fe (III) and complex with them, then the nucleation and crystallization occurred within the self-assembled structure of the organic matrices. So the crystallites had some certain oriented growth. The molecular structure and properties of polysaccharide and protein play an important role in the mineralization process. The mineralization behavior of Fe(OH)₃ gel was also influenced by pH, alkalinity, aging temperature, aging time etc. Different anions existing in the mineralization system could not change the mineralization process, but the morphology of the minerals were different.Dextran molecule could inhibit the iron oxide nucleus to free diffusion and growth by being absorbed onto their surfaces and enwrapping the nucleus fimly, so nanoscale P-FeOOH and a-Fe2O3 were obtained. P-FeOOH would be the transition phase of Fe(OH)3 gel and a-Fe2O3 . The transformation took place by the ways of dissolution/reprecipitation in the early stage. With the increasement of the concentration of dextran(up to 2wt%) in solution, the rate of crystal growth was accelerated.Chitosan molecule could modulate Fe(OH)3 gel to form nanoscale P-FeOOH. The nucleation occurred along with the chitosan backbone and formed a regular array of crystal structure. The morphology of minerals would be changed by different concentration of chitosan in the system, but nucleation and crystallization could be inhibited in higher concentration of chitosan.a-FeOOH was formed in the early stage of the mineralization system with Carboxymethylchitosan, then a-FeOOH disappeared gradually against aging time and a-Fe2O3 was formed eventually. There was a phase transformation from a-FeOOH toa-Fe2O3 during the mineralization process. The mode of interaction between Fe (III) and Carboxymethylchitosan was changed by different experimental method.With the increasement of the concentration of gelatin(up to lwt%) in solution, the formation of a-FeOOH in these mineralization systems were accelerated. The crystallites was arranged regularly in some certain direction and gelatin was absorbed on their surfaces. Dextran played an major role in the mineralization system with the mixture of gelatin and dextran(mole ratio is 1:1). It was related to the high hydrophily of dextran.In the simulative biomineralization system with Shaerotilus, iron biomineralization took place both inside and outside of the Shaerotilus cells. The crystal structure and morphology of iron minerals were similar to those formed in the mineralization system with dextran. It was further concluded that polysaccharide and protein could modulate iron biomineralization process.The results will help to give us an insight into the biomineralization mechanism which existed widely in nature, then provide theoretical instruction to develop a new type of material formed by iron biomineralization and apply to repair environment pollution.