The formation age and evolution of Kumtagh Desert

The ancient aeolian sand has been regarded as an indicator for the formation and evolution of a desert in the past.Kumtagh Desert is located at the northern fringe of Qinghai-Tibet Plateau.The first integrated scientific investigation to the desert was carried out during the period of 2004-2006.Kumtagh Desert is an ideal natural model for studying the formation and evolution of the desert because the Quaternary strata containing ancient aeolian sands are widely distributed.The integrated field investigation and studies on sedimentary,chronology and palynology of typical profiles named Suosuo gully,Xiaoquan gully and gravel body with ancient aeolian sand layers showed that Kumtagh Desert was probably formed as early as 2,097.7±314.7 ka BP.During the period of 386.9±58.0 ka BP to 285.9±42.9 ka BP,the desert largely expanded and formed its modern distribution pattern.The desert was originally developed in the southwest,subsequently,expanded to the north and northeast.The sedimentary facies of Suosuo gully profile revealed that the desert experienced at least 19 cycles of advance and inverse processes of desertification with an average period of 110 ka in the Quaternary.The neotectonic movements played an important role in the formation,development and geomorphology of the desert.On one hand,the movements caused the formation of intermontane fault basin,which was further developed towards the closed drought basin,and caused the formation of natural environment.On the other hand,under the control of surrounding faults,the unique broom-shaped desert landscape was formed,and the gullies and sand ridges in this region experienced an abrupt directional change from north by west to north by east at the location of 39°45＇-39°55＇N.The unique landscape of gravel body that occurred widely in the northern desert was formed after 285.9±42.9 ka BP.The results in this paper provide the scientific basis for studying the formation age and evolutionary process under the dry climate and environment in the northwestern China,and the uplifting of Qinghai-Tibet Plateau as well as its responses to the global climate changes.

Adsorption and Desorption Characteristics of Cadmium Ion by Ash-Free Biochars

The aim of this study was to investigate adsorption and desorption characteristics of cadmium ion(Cd(II))by ash-free biochars and the adsorption mechanism.Biochars were prepared using peanut shell,bamboo,and Sophora japonica Linn.Ash-free biochars were obtained by treating the biochars with acid elution.Adsorption and desorption data from batch experiments were analyzed using the Langmuir and Freundlich models and three adsorption kinetics models(i.e.,the Pseudo second-order,Elovich model,and the Intraparticle diffusion models).Results showed that the acid elution improved the pore structure of biochars,increased C content and aromatic functional group content,enhanced biochars hydrophobicity and adsorption capacity for Cd(II).Ash-free peanut shell biochar showed the best Cd(II)adsorption performance among the biochars.Adsorption of ash-free peanut shell biochar reached the equilibrium within 6 h with adsorption capacity of 34.2 mg/g.The adsorption conditions were optimized by orthogonal experiment.The Cd(II)removal efficiency achieved 91.7%with the optimized condition:initial concentration of Cd(II)of 50 mg/L,pH of 5,adsorption time of 12 h,and temperature of 15°C.Isothermal adsorption of Cd(II)by the six biochars was best described with the Langmuir model,indicating that the adsorption was a physical-chemical composite process.The desorption isotherm showed the hysteresis between adsorption and desorption.The main mechanism of Cd(II)adsorption of the ash-free biochars was a complex interaction of physical and chemical reactions,mainly including electrostatic adsorption,cationic-π,and ligand exchange.