The Synthesis Of Magnesium/Rare Earth Nitrate And The Influence On The Growth And Lipid Accumulation Of Chlorella

With the decrease of fossil energy and the environmental pollution caused by the burning of fossil fuels, biodiesel has attracted much attention as the environmental substitute product for fossil energy. Chlorella has great advantages and development potential as one of the important raw material for biodiesel production. In this paper, the solid-liquid equilibria of the Mg（NO₃）_2-Ln（NO₃）_3-HNO_3-H₂O （Ln= La, Ce, Pr, Nd, Sm, Eu, Tb） quaternary systems in the （～21%） HNO₃ regions at T= 298.15 K were studied by using the method of isothermal solubility, the phase diagrams were obtained based on the measured data, the new solid phase compounds 3Mg（NO₃）₂·2Ln（NO₃）₃·24H₂O （Ln= La, Ce, Pr, Nd, Sm） were found in the quaternary systems of Mg（NO₃）_2-Ln（NO₃）_3-HNO_3-H₂O （Ln-La, Ce, Pr, Nd, Sm）, while the Mg（NO₃）_2-Ln（NO₃）_3-HNO_3-H₂O （Ln= Eu, Tb） systems were found to be simple systems. The new solid phase compounds 3Mg（NO₃）₂·2Ln（NO₃）₃·24H₂O （Ln= La, Ce, Pr, Nd, Sm） were synthesized according to the phase chemical relation, then they were characterized by chemical analysis, X-ray diffraction （XRD）, X-ray diffraction single crystal structure analysis, and thermogravimetric/differential thermogravimetric （TG-DTG） techniques. The enthalpies of solution for the new solid phase compounds were measured with a heat conduction microcalorimeter, and their standard molar enthalpies of formation were calculated. For the compounds of 3Mg（NO₃）₂·2Ln（NO₃）₃·24H₂O, magnesium is an essential element of chlorophyll a, and it affect the photosynthesis of plant indirectly; the concentration of nitrogen have significant impact on the growth and lipid yield of Chlorella, it will promote the growth and lipid accumulation of Chlorella at a suitable concentration; in addition, the appropriate concentration of the rare earth element added also promote the growth of Chlorella. In order to explore the impact of magnesium/rare earth nitrate on the growth of Chlorella, different concentrations of rare earth/magnesium nitrate was added to the culture medium of Chlorella, the growth curves of algal cells were plotted, and the lipid content of Chlorella were measured.The main contents and results of this study are as follows:1. The solid-liquid equilibria of the Mg（NO₃）_2-Ln（NO₃）_3-HNO_3-H₂O 3Mg（NO₃）₂·2Ln（NO₃）₃·24H₂O （Ln= La, Ce, Pr, Nd, Sm, Eu, Tb） quaternary systems in the （～21%） HNO₃ regions at T= 298.15 K were studied for the first time by using the method of isothermal solubility, and the phase diagrams were obtained based on the measured data. The results of the study of Mg（NO₃）_2-Ln（NO₃）_3-HNO_3-H₂O （Ln= La, Ce, Pr, Nd, Sm, Eu, Tb） systems were regular: the new solid phase compounds 3Mg（NO₃）₂·2Ln（NO₃）₃·24H₂O （Ln= La, Ce, Pr, Nd, Sm） were found in the quaternary systems of Mg（NO₃）_2-Ln（NO₃）_3-HNO_3-H₂O （Ln= La, Ce, Pr, Nd, Sm）, while the Mg（NO₃）_2-Ln（NO₃）_3-HNO_3-H₂O （Ln= Eu, Tb） systems were found to be simple systems, it is the "Bicomponent effect" of the rare earth element.2. Comparing the reported ternary systems Mg（NO₃）_2-Ln（NO₃）_3-H₂0 （Ln= La, Ce, Pr, Nd, Sm） with the present quaternary systems, it can be found that the solubility values of rare earth nitrate and magnesium nitrate decreased observably in～21% HNO₃. The larger the nitric acid mass percentage included in the equilibrium liquid phase, the smaller the solubility values of rare earth nitrate and magnesium nitrate, it should be caused by common-ion effect.3. The XRD diffraction patterns for 3Mg（NO₃）₂·2Ln（NO₃）₃·24H₂O （Ln = La, Ce, Pr, Nd, Sm） are identical, which indicates that their crystallographic parameters should be very similar and their structures should be isomorphic. The single crystal structure analysis were undertaken and the crystal data were measured for the first time, and the results show that the five compounds all belong to hexagonal systems, with space group R3.4. The standard molar enthalpies of solution for the compounds of 3Mg（NO₃）₂·2Ln（NO₃）₃·24H₂O （Ln= La, Ce, Pr, Nd, Sm） were measured under the condition of infinite dilution for the first time, they are （107.96± 0.74） kJ·mol-1, （110.18±0.54） kJ·mol-1, （102.96±0.55） kJ·mol-1, （101.26± 0.77） kJ·mol-1 and （80.27±0.81） kJ·mol-1, respectively. And the standard molar enthalpies of formation of 3Mg（NO₃）₂·2Ln（NO₃）₃·24H₂O （Ln= La, Ce, Pr, Nd, Sm） were calculated to be-（12242.6±2.5） kJ·mol-1,-（12223.1± 2.4） kJ·mol-1,-（12232.6±2.5） kJ·mol-1,-（12214.13±2.5） kJ·mol-1 and-（12183.6±2.5） kJ·mol-1, respectively.5. Accordding to the thermal analysis of the solid phase compounds, 3Mg（NO₃）₂·2Ln（NO₃）₃·24H₂O （Ln= La, Ce, Pr, Nd, Sm） decompose to form 3MgO·La203,3MgO·2CeO2,3MgO·1/3Pr6O11,3Mg·ONd203,3Mg·OSm2O₃, which may be potential catalytic materials in some organic synthesis reactions.6. C. luteorividis, C. Protothecoides, C. Sacchrarophila, C. pyrenoidosa and C. vulgaris were used to explore the impact of rare earth/magnesium nitrate on the growth of Chlorella. It can be found from the experiments that 10-’mM and 10-6mM of 3Mg（NO₃）₂·2Ln（NO₃）₃·24H₂O （Ln= La, Pr） in the culture medium of Chlorella will inhibit the growth of Chlorella. But when the concentration of 3Mg（NO₃）₂·2Ln（NO₃）₃·24H₂O was 10-2mM,10-3 mM, 10-4 mM and 10-5 mM, it will promote the growth of Chlorella, and the growth promoting effect of 10-2mM 3Mg（NO₃）₂·2Ln（NO₃）₃·24H₂O added group was higher than that of other groups.7. The lipid content of Chlorella were measured by using the method of Bligh-Dyer, by comparing with the control group, it can be found that the lipid content of 10-2 mM 3Mg（NO₃）₂·2Ln（NO₃）₃·24H₂O （Ln= La, Pr） added group was slightly higher than that of control group, which indicates that 10-2 mM 3Mg（NO₃）₂·2Ln（NO₃）₃·24H₂O added in the culture medium of Chlorella not only can promote the growth of Chlorella, but also make no negative impact on the lipid content.