BIOGEOCHEMICAL PROCESSES OF PHOSPHORUS AND SILICON IN SOUTHERN BOHAI SEA SURFACE SEDIMENTS

Based on the author’s previously obtained results on P and Si forms in southern Bohai Sea surface sediments,this study mainly foucusing on the controlling factors, existence forms, and biogeochemical processes of P and Si showed that the transferable forms of phosphorus in sediments were mainly controlled by the mineralization of organic matters and the reduction of high valence iron; whereas the transferable forms of silicon were possibly controlled by the dissolution and precipitation as well as biochemical processes of living organisms.

Kinetics of Reaction-Crystallization of Struvite in the Continuous Draft Tube Magma Type CrystallizersmInfluence of Different Internal Hydrodynamics

A laboratory-scale reaction-crystallization process of struvite synthesis from diluted water solution of Mg^2＋, NH^＋ 4 and PO3- ions was studied. The research covered the tests of two original constructions of continuous jet-pump Draft Tube Magma （DTM）-type crystallizers with internal circulation of suspension （upward/downward）. Interactions between constructional, hydrodynamic and kinetic factors were established and discussed. Nucleation and linear growth rates of struvite crystals were calculated on the basis of population density distribution. Kinetic model of idealized Mixed Suspension Mixed Product Removal （MSMPR） crystallizer considering the size-dependent growth mechanism was applied （Rojkowski hyperbolic equation）. For comparison purposes the kinetic data corre- sponded to a simpler, continuous draft tube-type crystallizer equipped with propeller agitator were analyzed. It was concluded that crystal product of larger size was withdrawn from the jet-pump DTM crystallizer of the descending flow of suspension in a mixing chamber.

Reaction Crystallization of Struvite in a Continuous FB MSZ Type Crystallizer with Jet Pump Driven by Compressed Air

The results of struvite reaction crystallization from diluted water solutions of phosphates （V） （0.20 mass% of PO43-） by means of magnesium and ammonium ions are presented. Continuous FB MSZ crystallizer with jet pump driven by compressed air was used. Influence of pH and mean residence time of suspension on the crystal product quality was determined. Increase in pH from 9 to 11 resulted that mean crystal size decreased nearly two-time： from 27.1 to 15.1μm for mean residence time of suspension 900 s. Elongation of this time from 900 to 3,600 s influenced struvite crystal size advantageously-it increased from 27.1 to 41.2 μm at pH 9. From the population density distributions nucleation and growth rates of struvite were calculated based on the simplest SIG model of mass crystallization kinetics in MSMPR crystallizer. Linear growth rate ofstruvite crystals decreased nearly two-time with the increase in environment pH from 9 to 11, and more than 2.5-time with the elongation of mean residence time of crystal suspension in a crystallizer from 900 to 3,600 s from 1.34× 10-8 m/s （pH 9, τ= 900 s） to 2.60×10-9 m/s （pH 11, τ= 3,600 s）.

Roller-coaster atmospheric-terrestrial-oceanic-climatic system during Ordovician-Silurian transition:Consequences of large igneous provinces

The Ordovician-Silurian transition(OST)hosted profound and frequent changes in the atmospheric-terres trial-oceanic-climatic system(ATOCS).Previous studies have found contrasting stages for such changes,primarily based on hiatus-interrupted sections.However,the dominant driving factors and mechanisms reconciling such frequent changes remain controversial.Mercury isotopes,which undergo both massdependent and mass-independent fractionation,can provide critical insights into the deep-time ATOCSs,especially for those impacted by large igneous provinces(LIPs)events.Here,we build a highresolution multi-proxy record of Hg(concentrations and isotopic compositions)combined with organic carbon isotopes(δ^(13)Corg)and whole-rock geochemical data(including trace elements and phosphorus)from continuous cores in the Yangtze Platform,South China.Our data,combined with reported ones,indicate the occurrence of LIP eruptions against localized volcanism,and four successive,yet contrasting stages of ATOCSs during the OST.Moreover,we identified the coupling between two-pulse LIP magmatism and extreme ATOCSs,each with special pCO_(2),weathering rate,primary productivity,redox condition,climatic mode,and biotic evolution.For stage I,the first pulse of LIP magmatism triggered global warming,enhanced terrestrial weathering,oceanic acidification,eutrophication,anoxia,P recycling,and thereby widespread deposition of black shales.During stage II,the Hirnantian glaciation and oxygenation arose from the intense chemical weathering and black shale deposition of stage I;slashed terrestrial weathering and oceanic oxygenation facilitated CO_(2) accumulation.In stage III,another pulse of LIP magmatism triggered the de-glaciation,and the ATOCS was largely similar to that of stage I.This led to another round of oxygenation and positive d13Corg excursion in stage IV.Compared with the environmental pressure by the peculiar ATOCS of each stage,their transitions might have been more devastating in triggering the prolonged Late Ordovician Mass Extinction(LOME).Moreover,limited biotic recovery was possible in the later portion of stages I and III.The multi-proxy study of continuous strata of the OST provides an excellent framework for better illuminating LIPs’essential role in driving the“roller-coaster”behavior of the ATOCS and thus biotic crisis during the pivotal period of the OST.