Reductive Reactivity Of Iron-Bearing Minerals In Soil Remediation

With the developmentment of China economy,the soil environment is deteriorated sharply,which is the container of matter and energy in the earth and also the collection of contamination.There are numerous soil remediation measures home and abroad,however,soil contamination still has no great improvement for the finite effect on the polluted soils.The iron-containing minerals in soil constitutes certain natural self-clean capability,which would take on large significance to soil remediation through the investigation of reductive reactivity of iron-containing minerals in soil and means to strengthen.The soil natural reductive capacity was firstly investigated in the paper,in which the main reductive substance in the soil and the effect factors of soil reduce capacity were analysed in details,particularly the reduce capacity of Green Rust,the potential iron-containing minerals in the soil.Then the reductive properties of Cr(â…¥)and o-chloronitrobenzene(CNB)by soil and Green Rust were studied.After a great many of experiments,a effective means for measuring the soil reduce capacity were obtained.Firtly the physical-chemical characters of fluvo-aquic soil and paddy soil were studied and then the reductive properties of Cr(â…¥)and o-chloronitrobenzene(CNB) by natural soils.The free,amorphous iron oxide and organic matters content in fluvo-aquic soil were obviously lower than those in paddy soil.And the reduce capacity of fluvo-aquic soil was merely 65.9%of that of paddy soil,for the content in soil of reductive organic matters and iron-containing minerals plays a crucial role in the soil reduce capacity,as well as the existing condition of them.The reductive capability of natural soils to CNB was extremely weak but promoted distinctly after the iron-containing minerals were added into soilGreen Rust is probably the iron-containing minerals existing in the soils.The appropriate methods to prepare Green Rust sulfate(GR_SO4)and Green Rust carbonate(GR_CO3)were summarized referring to materials and a great number of experiments.Then the reductive characters of Green Rust to Cr(â…¥)and CNB were investigated.The reduce capacity of GR_SO4and GR_CO3measuring by Cr(â…¥)were respectively 1093.1å’Œ873.7μmol/g;The reduce capacity of GR_SO4and GR_CO3 measuring by CNB were respectively 81.2 and 30.3μmol/g.The reduce capacity of GR_SO4was obviously larger than that of GR_CO3owing to the structural difference in two types of Green Rust.The effect of pH on soil and Green Rust was studied.A great deal of protons were consumed in the course of Cr(â…¥)reduction.Therefore the soil reductive capability fell down gradually while the soil pH rose(pH=3⁹),for a lower pH value can promote Cr(â…¥)reduction.The Eh of Green Rust reduced going with pH rose and Fe(â…¡)could transform to adsorption and complex states minerals,which hold stronger reductive capability,so reductive capability of Green Rust increased visibly and the production quantity of one kind of its reductive production,o-chloroamline, also increased greatly.The primary production of soil and green rust was Cr³⁺,which probable tranformed to Cr(OH)²⁺å’ŒCr(OH)⁺ with the change of pH in the solution.The o-chloroaniline(CAN),o-chloroazoxybenzene and o-chloroazobenzene were detected by GC-MS in the reaction solution of Green Rust and CNB.However no chlorine ion was detected from the production.Meanwhile,Green Rust was oxidated to various iron-containing oxide hydroxide and hydrate complex such as Fe(SO₄)(OH)·6H₂O,Fe₃O₄,FeOOH,and then gradually transformed to magnetite,goethite or other iron-containing minerals complex after a long period.The means to strengthen soil reductive capability were studied.It could promote the soil reduce capacity that green rust,Fe²⁺,pyrite cinder,magnetite or iron paring is mixed into soil.In the experiment of reducing Cr(â…¥),the soil with Fe²⁺or Green Rust had higher reduce capacity.In the experiment of reducing CNB,the soil with iron paring and Green Rust had higher reductive capacity,as well as the soil with Green Rust had some slow-release ability and maintained higher reduce capacity for a long period.The iron-containing minerals in soil constitutes a larger reduction to toxic contamination.The combination soil remediation of physical-chemical and biochemical means will be realized by the process of degrading the toxicity of contamination with iron-containing minerals ruduction,decreasing biological inhibition and enhancing the degradation capability of soil contaminations by microorganism in soil.