A Comparative Research On Boron Isotope Behavior Of Carbonate Sedimentary And Clay Mineral Adsorption Phases In Sediments

The study of boron content and isotopic composition of clay minerals and carbonates in marine sediments laid the foundation for elucidating the geochemical cycle of boron in the marine environment.However,current research methods are difficult to distinguish between actual sediment samples when they are studied.It is questioned whether the comprehensive information reflected by the boron phase of the carbonate sedimentary phase and the adsorption phase of boron in the clay mineral is consistent with the information they reflect.In order to determine if the information of boron in clay minerals and calcium carbonate is consistent,in this paper,independent inorganic calcium carbonate deposition and clay mineral adsorption experiments were performed simultaneously in the same mother liquor.In order to determine if the information of boron in clay minerals and calcium carbonate is consistent,we conducted independent inorganic calcium carbonate deposition and clay mineral adsorption experiments simultaneously in the same mother liquor to compare the differences between clay minerals and calcium carbonate.At the same time,the effects of Boron concentration,temperature and pH on the behavior of boron incorporation of calcium carbonate and clay minerals were investigated.Extraction of boron from clay minerals and calcium carbonate by acid-solubilization.Boron special effects resin and anion-cation mixed resin are used to separate and purify boron.The isotopic composition of boron was determined with a Triton thermal ionization solid isotope mass spectrometer.The experimental results of boron concentration show that the content of clay minerals and calcium carbonate boron increases with the increase of boron concentration in the mother liquor.When the mother liquor boron concentration increased from 21.82ppm to 148.84ppm,the boron content of the clay mineral mixture increased from 20.14ppm to 107.91 ppm,and the calcium carbonate boron content increased from 115.76ppm to 510.77ppm.In the same mother liquor,the calcium carbonate boron content is significantly higher than that of clay minerals.The boron content of calcium carbonate is about 5 times that of clay minerals.The boron isotope compositions of clay minerals and calcium carbonate do not change with the concentration of boron in the mother liquor,but the boron isotope composition of calcium carbonate(27.08?-27.99)is significantly higher than that of clay minerals(-35.00?-35.47).This indicates that the B(OH)3 fraction incorporated into calcium carbonate is greater than that of clay minerals.The temperature experiment results show that the boron content of calcium carbonate decreases with the temperature of the mother liquor.When the temperature of the mother liquor increased from 10 ? to 33 ?,the calcium carbonate boron content decreased from 54.75 ppm to 40.09 ppm.The boron content of the clay mineral does not change with the temperature of the mother liquor.The boron content of the clay mineral mixture varies from 10.69 ppm to 12.36 ppm.In the same mother liquor,the calcium carbonate boron content is significantly higher than that of the clay mineral.The boron isotope composition of calcium carbonate decreases as the temperature of the mother liquor increases,from-29.29 at 10?.to-31.38 at 33?.It shows that high temperature will inhibit the incorporation of B(OH)3 into calcium carbonate.The boron isotope composition of the clay mineral increases with temperature,the boron isotope composition of the clay mineral mixture increased from-34.36 to-32.20.This may be due to the influence of temperature on the boron isotope fractionation between B(OH)3 and B(OH)4-in the mother liquor.In the same mother liquor,the boron isotope composition of calcium carbonate is higher than that of clay minerals.This indicates that the B(OH)3 fraction incorporated into calcium carbonate is greater than that of clay minerals.The results of pH test showed that the clay minerals and calcium carbonate boron content increased with the increase of the mother liquor pH,and the calcium carbonate boron content(15.96ppm?104.76ppm)increase is significantly higher than the clay mineral mixture(16.61ppm?35.60ppm).The boron isotope composition of clay minerals and calcium carbonate increases with the pH of the mother liquor.Although the difference between them is not obvious,the boron isotope composition of calcium carbonate(-30.67?-23.80)is still higher than that of the clay mineral mixture(-32.35?-25.26).It can be seen that there is a difference in the behavior of boron in the adsorption phase of clay minerals and in the calcium carbonate deposition phase,and their integrated boron information does not reflect real environmental information.The results of this study provide scientific basis for the use of boron isotopes in sediments for palaeoclimatic and paleoenvironmental studies that require or do not require separate extraction of boron from the sedimentary facies and adsorption phase boron.