氮是水生生态系统中重要的营养元素,沉积物中氮的释放是上覆水中氮的重要来源和决定性因素[1],对湖泊生态系统氮循环及由氮内源负荷引起的富营养化具有重要影响,而间隙水中各形态氮在沉积物-水界面氮循环系统中也扮演重要角色[2-3]。本文针对沱江流域金堂地区冬季沉积物,开展了河流沉积物中总氮（total nitrogen,TN）、可交换氨氮（ammoniacal nitrogen,AN）、有机氮（organic nitrogen,ON）及间隙水中总溶解态氮（total dissolved nitrogen,TDN）、氨氮（ammonia nitrogen,NH4+-N）、亚硝态氮（nitrite nitrogen,NO2--N）、硝态氮（nitrate nitrogen,NO3--N）的赋存形态系统分析测定,并与十年前该河流相关结果进行研究分析。实验结果表明:水体中Ammonium2017、Nitrate-N2017、DON2017、TDN2017的含量是减少的,Nitrite-N2017的含量增加了3倍,各氮形态在上覆水体中的含量小于在间隙水中的含量,且随着上覆水深度的增加而逐渐减小;沉积物中AN的含量明显增加,ON的含量明显减少,TN的含量略有增加,推测:简阳地区沉积物作为氮的汇不断吸收间隙水甚至上覆水中的氮,ON和AN之间存在相互转换关系,总体来说,氮是由水体进入到沉积物中,水体中氮的污染得到了缓解。

沉积物-水界面上不仅发生着沉积作用,还发生着沉积后作用,即早期成岩作用[1]。早期成岩过程中有机质的降解是沉积物早期成岩反应的最主要驱动因素,其常常伴随着SO42-的还原,与铁生成各种形态的铁硫化物[2]。硫酸根的还原产物为S2-,游离态的S2-进入间隙水中以H2S形式扩散,可被O2、铁锰氧化物氧化为中间态S0,也可与铁氧化物还原产物Fe2+发生反应生成FeS,FeS形态不稳定,在S0的存在下,可转变为更稳定态的Fe3S4和FeS2[3]。本论文针对长江五大支流之一的沱江,研究了其上游金堂段及中游简阳段的沉积物中还原性无机硫的垂向分布特征,主要包括元素硫（Elemental sulfur,ES）,酸挥发性硫（Acid volatile sulfides,AVS）以及硫化矿物硫（Mature pyrite sulfur,MPS）。研究结果表明,简阳地区ES,AVS以及MPS的平均含量均小于金堂地区。金堂地区MPS＞ES＞AVS;简阳地区ES＞MPS＞AVS。简阳段沉积物中AVS含量相对金堂较低,由于与重金属不易形成金属硫化物,重金属在间隙水中的浓度较高,容易被生物所富集,潜在的生物毒性较金堂段大。MPS作为稳定的FeS2的形式在沉积物中被埋葬下来,暂时退出硫的地球化学循环。AVS/MPS的比值可以用来评价AVS向MPS的转化,当该比值低于0.3时,反映了AVS可以有效的转化为MPS[4]。本论文中沱江金堂段和简阳段AVS/MPS的比值基本都大于0.3,反映了AVS向MPS继续转化的可能性较小。

Densities of the sodium arsenate aqueous solution with the molality varied from (0.04165 to 0.37306) mol · kg-1 were determined experimentally at temperature intervals of 5 K from 283.15 K to 363.15 K and ambient pressure using a precise Anton Paar Digital vibrating-tube densimeter. The apparent molar volumes (V φ), thermal expansion coefficient (α) and partial molar volume (V ¯ B) were obtained based on the results of density measurement. The 3D diagram of apparent molar volume against temperature and molality as well as the diagram of thermal expansion coefficient and partial molar volume against molality were plotted, respectively. On the basis of the Pitzer ion-interaction equation of apparent molar volume model, the Pitzer single-salt parameters ((βM,X(0)v, βM,X(1)v, βM,X(2)v and C M,Xv, M X = Na3 AsO4) and their temperature-dependent correlation F(i, p, T) = a 1 + a 2ln(T/298.15) + a 3(T - 298.15) + a 4/(620 - T) + a 5/(T - 227) (where T is temperature in Kelvin, a i is the correlation coefficient) for Na3AsO4 were obtained on account of the least-squares method. Predictive apparent molar volumes agree well with the experimental values, and those results indicate that the single-salt parameters and their relational coefficients of temperature-dependence for Na3AsO4 obtained are reliable.
© 2020 IUPAC & De Gruyter.

Densities of the sodium arsenate aqueous solution with the molality varied from (0.04165 to 0.37306) mol · kg-1 were determined experimentally at temperature intervals of 5 K from 283.15 K to 363.15 K and ambient pressure using a precise Anton Paar Digital vibrating-tube densimeter. The apparent molar volumes (V φ), thermal expansion coefficient (α) and partial molar volume (V ¯ B) were obtained based on the results of density measurement. The 3D diagram of apparent molar volume against temperature and molality as well as the diagram of thermal expansion coefficient and partial molar volume against molality were plotted, respectively. On the basis of the Pitzer ion-interaction equation of apparent molar volume model, the Pitzer single-salt parameters ((βM,X(0)v, βM,X(1)v, βM,X(2)v and C M,Xv, M X = Na3 AsO4) and their temperature-dependent correlation F(i, p, T) = a 1 + a 2ln(T/298.15) + a 3(T - 298.15) + a 4/(620 - T) + a 5/(T - 227) (where T is temperature in Kelvin, a i is the correlation coefficient) for Na3AsO4 were obtained on account of the least-squares method. Predictive apparent molar volumes agree well with the experimental values, and those results indicate that the single-salt parameters and their relational coefficients of temperature-dependence for Na3AsO4 obtained are reliable. © 2020 IUPAC & De Gruyter.

Combining of the determined solubilities of two ternary systems NaCl–SrCl 2 –H 2 O and KCl–SrCl 2 –H 2 O and Pitzer binary parameters obtained in the literature at different temperatures,the lacking Pitzer mixing parametersθ Na,Sr ,θ K,Sr ,Ψ Na,Sr,Cl ,andΨ K,Sr,Cl were fitted on the basis of the Pitzer model.The variable temperature chemical model for Pitzer mixing parameters including Sr^2+ ion was built.The model was then used to calculate thermodynamic properties such as the solubilties,osmotic coefficients,ionic activity coefficients and dilution enthalpy of the quaternary system NaCl–KCl–SrCl 2 –H 2 O in the wider temperature range.The theoretical results using the model coincide with the experimental values.The phase diagrams and Pitzer model for the quaternary system were then used to conduct computer simulation of isothermal evaporation and brine separation.The evaporation-crystallization route and the order of salt crystallization were obtained using the model at 298.15 K.The pure salts KCl,NaCl and SrCl 2 ·6H 2 O were separated from the solution with the model at 273.15 K and 323.15 K.The salts KCl,NaCl and SrCl 2 ·6H 2 O were separated from the solution with the model at 273.15 K and 323.15 K.This simulation results can supply fundamental data for salt separation and purification of brine systems.

The metastable zone width （MZW） of lithium metaborate salts and sodium metaborate salts at various concentrations was determined with the laser technique.The solubility data for lithium metaborate salts and sodium metaborate salts were investigated from 303.15 K to323.15 K with the isothermal dissolution method.The MZW of metaborate salts decreased with stirring rate increasing,but increased remarkably with increasing cooling rates and increasing concentration of sodium chloride.The apparent secondary nucleation order for metaborate salts was obtained using Ny?vlt’s approach.The apparent secondary nucleation order m of lithium metaborate salts is 4.00 in a pure Li BO 2 -H 2 O system with improved linear regression method,and 2.15 for NaBO 2 -H 2 O system.For Li BO 2 -H 2 O system,the corresponding equilibrium salts for saturated solution at 313.15 K and 323.15 K is Li BO 2 ·2H 2 O,and at 303.15,it is LiBO 2 ·8H 2 O,but the salts precipitated from the solution is LiBO 2 ·8H 2 O in the MZW experiments.It is NaBO 2 ·4H 2 O both for the saturated solution and crystallization from the solution for the system NaBO 2 -H 2 O.The results can provide theoretical direction and important data for the comprehensive development of metaborate salts from brine.

Rare alkaline metal cesium （Cs） along with its compounds has drawn increasing attention in recent years owing to its wide applications in the fields of catalyst,medicine,electronic technology and aerospace^[1] .In China,brine resources are abundant and distributed widely in the Qinghai-Tibet Plateau,which often exist with the complex salt-water system (Li^+ ,Na^+ ,K^+ ,Cs^+ //Cl^- ,SO 4 ^2- -H 2 O).As we all know,the phase diagram of the salt-water system can provide essential fundamentals for the separation and purification process for minerals.Therefore,in order to develop advanced methods for more effective and efficient extraction of Cs from aqueous solutions,the phase equilibrium study on the salt-water system containing Cs^+ is highly desirable^[2] .In this paper,we carried out the solid-liquid phase equilibria of ternary system （CsCl+Cs 2 SO 4 +H 2 O） at （288.15 and 308.15） K with isothermal dissolution method and the corresponding physicochemical properties （refractive index,density and p H value） were determined,and the corresponding phase diagrams at two temperatures were plotted.The system belongs to the hydrate I type.It was found that there are all one invariant point,two univariant curves,and two crystallization regions corresponding to cesium chloride and cesium sulfate at both temperatures.There are no double salts or solid solution in this system.

Phase equilibria in the quaternary system (Li 2 B 4 O 7 +Na 2 B 4 O 7 +Mg 2 B 6 O 11 +H 2 O) at 303.15K were studied experimentally by using the method of isothermal dissolution equilibrium.The inderite was synthesized by using magnesium sulfate and sodium tetraborate decahydrate reacting in an oil bath at temperature of 40 ^o C.Before the experiment,the synthesized inderite was determined by X-ray diffraction.The correlative phase diagrams were plotted by using the origin based on the experiment data.The solid phases were also determined by the method of X-ray diffraction.The quaternary phase diagram consists of an invariant point,three stable solution isothermal curves,and three solid crystallization regions.The solid phase of the system include Mg 2 B 6 O 11 ·15H 2 O,Na 2 B 4 O 7 ·10H 2 O,Li 2 B 4 O 7 ·3H 2 O.As is known,there are three different forms of magnesium borate,hungchsaoite,trilateral ascharite,and inderite.It’s reported that when in water,hungchasaoite and trilateral ascharite would be slowly converted to inderite with stirring and dissolution.It indicates that different forms magnesium borate will eventually be transformed into inderite.Therefore,inderite is the most stable magnesium borate.

Water activities for the ternary system of Li Cl-SrCl 2 -H 2 O were elaborately measured using an isopiestic method at 323.15 K.The osmotic coefficients were determined based on the lithium chloride and sodium chloride reference standards.On the basis of Pitzer original and its extended model,the Pitzer binary parametersβ^（0） ,β^（1） C^（0） and C^（1） for the systems Li Cl–H 2 O and SrCl 2 –H 2 O and mixing parameters ofθ Li,Sr andψ Li,Sr,Cl were fitted with the measured osmotic coefficients.The solubilities for the LiCl-SrCl 2 -H 2 O system were determined with the isothermal equilibrium method.The phase diagram of the system consists of three crystallization areas corresponding to Li Cl·H 2 O,SrCl 2 ·2H 2 O and SrCl 2 ·6H 2 O.A comparison of the phase diagrams at273.15,323.15,and 373.15 K shows that the areas of strontium chloride salts decrease obviously and SrCl 2 ·6H 2 O disappears at high temperature.The model was used to calculate the solubilties and water activities of the system.The agreement between the calculated data and experimental results for the ternary system indicates that the mixing parameters obtained in this work are reliable.The thermodynamic data obtained in this study are essential for development of universal thermodynamic models for brine systems containing lithium chloride and strontium chloride.

The solid-liquid phase equilibria in the systems NaCl–SrCl 2 –H 2 O and NaCl–CaCl 2 –SrCl 2 –H 2 O at 323.15 K were studied with the isothermal dissolution method.The solid-liquid equilibrium phase diagrams were constructed with the experimental results.A comparison of the diagrams of system NaCl–SrCl 2 –H 2 O from 288.15 to 373.15 K shows that area of strontium chloride salt region decreased obviously whereas the areas of NaCl almost invariant.The dry-salt diagram of the NaCl–CaCl 2 –SrCl 2 –H 2 O system consists of four single-salt crystallization regions for NaCl,SrCl 2 ·6H 2 O,SrCl 2 ·2H 2 O and CaCl 2 ·2H 2 O,five univariant solubility curves and two invariant points.Combining Pitzer binary parameters obtained in the literatures,the Pitzer mixing parametersθ Na,Sr ,θ Ca,Sr ,Ψ Na,Sr,Cl andΨ Ca,Sr,Cl were fitted with the solubility data in this study and literatures.The model was then used for predicting the solubilties of the two systems.The experimental solubilities in above two systems agree with the theoretical results calculated with the Pitzer parameters and equilibrium constants of the salts from the literatures These results on phase diagrams and thermodynamic models of system NaCl–CaCl 2 –SrCl 2 –H 2 O at can supply theoretical reference for strontium salts separation from chloride type brine.