Structural Characteristics And Copper Ion Adsorption Behaviors Of Humic Substances In Several Typical Zonal Soils Of China

Humic substances,the largest pool of organic matter in soil,are highly chemically reactive but recalcitrant macromolecular compounds.Humic substances(HS)play an important role in controlling the environmental behaviors of metal ions.The knowledge of chemical structure of humic substances is crucial for understanding their role in soil,as well as their interaction mechanisms with metal ions.This paper researched two aspects from quantity and strcture about humus substances in soil,as well as the adsorption of Cu2+ on humus components derived from an Alfisol in Norteast China.The results as below:1?The experiment which based on brown coniferous forest soil,dark brown soil,brown soil,yellow brown soil,yellow soil,latosolic red soil,and seven of laterite types were used for the test soil.In this paper,soil humus was divided into different components by modified Pallo method,in order to study quantity and optical characteristics of humus.Results showed that the carbon contents of HM were the highest,followed by humic acid and fulvic acid in soil humus.In humin fractionation,the carbon contents of HUr were the highest,followed by HUi and HUc.In different soil types,the carbon contents of dark brown soil were the highest in HA and FA,while latosolic red soil were the lowest.The carbon contents of brown coniferous forest soil were the highest in HM,while dark brown soil were the lowest.The carbon contents of dark brown soil were the highest in HUi and HUc,of which latosolic red soil of HUi were the lowest and brown coniferous forest soil of HUc were the lowest.The value of HA/FA and HUi/HUc were the highest in dark brown soil,while latosolic red soil were the lowest.The value of E4/E6 and ?logk of HUi was higher than HUc in brown coniferous forest soil,dark brown soil,brown soil and yellow soil,however,yellow brown soil,latosolic red soil and laterite was opposite.In HUi,the value of HA/FA and HUi/HUc was the highest in dark brown soil,latosolic red soil was the lowest.In HUc,the value of HA/FA and HUi/HUc was the highest in yellow brown soil,brown soil was the lowest.The result showed that the degree of humification of dark brown soil was the highest and latosolic red soil was the lowest.At the same time,the molecular structure of the HUi in latosolic red soil was the most complex and dark brown soil is the most simple,the molecular structure of the HUc in brown soil was the most complex andyellow brown soil was the mostsimple.2 ? The elemental analysis,solid-state carbon-13 cross-polarization magic-angle-spinning nuclear magnetic resonance and pyrolysis-gas chromatography/mass spectrometry(Py-GC/MS)techniques were used to measured the structural characteristics of humin and humic acid from dark brown soil,brown soil and latosolic red soil.Results showed that HU of brown soil and latosolic red soil was more aliphatic and stable,whereas less polar and aromatic compared with HA.That was opposite with the regularity of HA and HU derived from dark brown soil.Compared with latosolic red soil,aliphatics was higher for HA and HU in brown soil,whereas stability and polarity were lower,as well as aromatics.In this study,six humic substance fractions,including humic acid(HA),fulvic acid(FA),humin(HU),iron-bound HU(HUi),clay-bound HU(HUc)and residual HU(HUr),were sequentially extracted from an Alfisol of China.The elemental analysis,solid-state carbon-13 cross-polarization magic-angle-spinning nuclear magnetic resonance(13C CPMAS NMR)spectroscopy and pyrolysis-gas chromatography/mass spectrometry(Py-GC/MS)techniques were used to characterize these humic substance fractions.Among the six humic substance fractions,the proportion of aliphatic hydrocarbons in HUc and the proportion of phenols in HA were the highest,whereas the proportions of aliphatic hydrocarbons,aromatic compounds and lignin derived compounds in FA and the proportion of phenols in HUc were the lowest.The aliphaticity of FA was the highest,followed by HU and its components,and the lowest for HA.HUc was mainly responsible for the high abundance of aliphatic hydrocarbons of HU,whereas HUr was responsible for the high abundance of carbohydrates of HU.The sequential extraction procedure is useful for understanding the distinctions of the structural characteristics among different HS fractions and their interactions with metal ions,especially mineral-associated humin fractions.3 ? Results of the adsorption of Cu2+ on humin derived from brown soil and latosolic red soil,as well as six humus substances derived from dark brown soil,were studied by the batch equilibrium method showed that humin adsorption of Cu2+increased with temperature and initial Cu2+ concentration in all humic substances components at the different concentration of metal irons and tempreatures.Freundlich equation provided a best fit for the adsorption process.Thermodynamic parameters showed that the adsorption of Cu2+ on soil is spontaneous,endothermic andincreasingly disordered process.The isosteric heat of adsorption increased with initial Cu2+concentration.Humin and humic acid had energetically heterogeneous surfaces for the adsorption of Cu2+,and the surface energy heterogeneity of humin from latosolic red soil was greater than that from brown soil,at the same times,the surface energy heterogeneity of humin from dark brown soil was greater than that humic acid.Based on the Langmuir equation,the adsorbing capacity values were in the order FA>HUi>HA>HUc>HU> HUr,whereas this order in Freundlich equation were FA>HUi>HA>HU>HUc>HUr,which means that the result was similar.4?Relationships between structural characteristics and Cu2+ adsorption isotherm parameters of HS fractions were examined.Among these HS fractions,HA contained the highest proportion of phenols,FA has the lowest proportion of aliphatic hydrocarbons,and HUc exhibited the highest proportion of aliphatic hydrocarbons and the lowest proportion of phenols.HUc and HUr were mainly responsible for the high abundance of n-alkanes/n-alkenes and polysaccharides in HU,respectively.Adsorption of Cu2+ on HS fractions was fitted better with Langmuir and Frendlich isotherms.The maximum amounts of Cu2+ absorbed on HS fractions was positive correlated with O/C ratio and carbonyl C whereas negative correlated with C/N ratio(p < 0.01).The Langmuir constant k L was positive correlated with C/N ratio,and the Frendlich constant n was positive correlated with C/N ratio and polysaccharides whereas negative correlated with aromatics(p < 0.01).