不同碳酸盐岩对铅锌冶炼废渣-黑麦草体系中重金属迁移的影响

为探究岩溶环境制约下贵州喀斯特地区广泛存在的碳酸盐岩对铅锌冶炼废渣-黑麦草体系中重金属生物有效性的影响,本文以黔西北土法炼锌废渣为研究对象,通过盆栽实验向改良后的废渣中施加两种典型天然碳酸盐岩(石灰岩、白云岩)及其主要成分的化学品(碳酸钙、碳酸镁),经种植黑麦草培育3个月后分析废渣基质中Cu、Pb、Zn、Cd等重金属的形态变化与植物富集转运系数。结果表明:处理前铅锌废渣中Pb、Zn、Cu、Cd的总量分别为17 682、8 427.2、2 066、174.8 mg/kg,Cd的酸溶态比例最高,环境风险较大。与对照相比,施用天然碳酸盐岩(石灰岩、白云岩)或其主要化学成分的化学品(碳酸钙、碳酸镁)后均显著降低了铅锌废渣中酸溶态Cu、Pb、Cd的比例并增加了残渣态Zn的比例,5种添加物(石灰岩、白云岩、钙盐、镁盐、混合碳酸钙镁)施用均不同程度地增加了铅锌废渣中残渣态Cd的含量。添加量为4g/kg(即0.4%)时,与对照相比,5种添加物使黑麦草根和叶片中重金属Cd分别降低了3.62%～29.54%和28.21%～43.59%。冗余分析表明,根中Ca、Mg与酸溶态Cu、Pb、Zn、Cd呈显著性负相关;两种典型碳酸盐岩(石灰岩和白云岩)及其主要成分的化学品添加形成的岩溶环境制约下,铅锌冶炼废渣-黑麦草体系中多种重金属的生物有效性受到明显抑制,可有效减弱其上所种植物黑麦草对重金属的吸收。相关结果对喀斯特地区矿冶废渣堆场重金属污染的原位控制、矿山复垦及生态修复具有一定的理论参考和实践价值。     

西南碳酸盐岩石质山地土壤-植被系统中矿质养分不足问题的思考

本文提出了矿质养分不足可能是西南石漠化喀斯特山地植被生产力低和植被修复困难重要原因的观点。桂西北环江喀斯特农业生态站和黔中清镇王家寨小流域碳酸盐岩石灰土坡地的平均土壤质量厚度(<2mm),分别为21.95kg/m2和16.04kg/m2。以地上部分生产力4.8t/ha.a,灰分含量9.5%计,植被每年要从土壤中吸取45.6g/m2.a的矿质养分,相当于两地土壤总量的约千分之二。土壤总量少导致的西南碳酸盐岩石质山地土壤矿质养分不足,可能是植被生产力低下的重要原因。纯碳酸盐岩硅酸盐矿物含量低,成土速率低。长期不断的收获植物,不可避免地要带走矿物质,导致喀斯特山地土壤矿质养分的减少,进而抑制植物生长.施用矿质肥料可能是促进喀斯特石质山地植被修复的重要措施。     

珠江流域水化学组成的时空变化特征及对岩石风化碳汇估算的意义

基于水-岩-气-生相互作用的碳酸盐风化碳汇模型表明,陆地碳酸盐风化碳汇是大气CO_2汇的重要组成部分;然而,碳酸盐风化碳汇的过程、机制和控制因素仍有待进一步的研究。本文采用野外监测、现场滴定和样品室内测试相结合的方法,对珠江流域支干流分旱季和雨季进行了4次野外监测取样,研究其水化学组成的时空变化特征。结果表明:珠江流域支干流的水化学组成受流域岩石风化、气候和水生光合作用的共同影响,并具有明显的时空变化特征。空间上,南盘江下游双江口段至红水河上游蔗香段,水流较慢,水质清澈,水生光合作用强烈,电导率、[HCO_3~-]和[Ca~(2+)]的空间变化主要受水生光合作用控制;从红水河上游蔗香段至肇庆西江大桥监测点,反映的是流域岩石风化对水化学空间变化的影响。季节变化上,西江的电导率、[HCO_3~-]和[Ca~(2+)]呈现出夏季低、冬春季高的特征,主要反映稀释效应的控制。西江干流河水的溶解氧具有明显的季节变化,在上述南盘江下游双江口段至红水河上游蔗香段,DO是夏季高冬季低,其他监测点是冬季高而夏季低;DO的季节变化受水生光合作用强度的控制。在南盘江下游双江口段至红水河上游蔗香段,温度是光合作用强度的限制因子,而其他监测点的光合作用限制因子为浊度影响的光照。造成上述差异的原因是监测点的水文环境不同。通过对梧州水文站流量和[HCO_3~-]变化的分析发现,[HCO_3~-]的季节变化幅度相对流量小得多,显示在西江流域中,HCO_3~-也存在化学稳定性行为。因此在西江流域中,流量变化是岩溶碳汇通量变化的主控因子。研究还发现,西江流域中具有强烈的生物碳泵效应,由内源有机碳形成的碳汇通量约占传统计算模式碳汇(溶解无机碳-DIC)通量的40%。因此,在估算珠江流域碳酸盐风化碳汇时,必须考虑水生生态系统光合生物对DIC的利用形成的有机碳的贡献。     

以PEG为模板剂制备Bi_2O_2CO_3及其可见光光催化性能

以聚乙二醇-6000(PEG-6000)为模板剂水热法制备碳酸氧铋(p-Bi2O2CO3)粉末,采用X射线衍射(XRD)、扫描电镜(SEM)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)和紫外可见漫反射(DRS)对粉末进行了初步表征。在可见光(λ≥420 nm)照射下,以罗丹明B(RhB)和水杨酸(SA)光催化降解实验为探针反应,实验结果表明,p-Bi2O2CO3具有较高的光催化活性,对RhB和SA有较好的降解效果。通过紫外-可见光谱(UV-Vis)、红外光谱(IR)和测定总有机碳(TOC)含量,光催化反应35 h后RhB的矿化率为77%,同时对SA的降解率达到43%。同时,采用N,N-二乙基对苯二胺(DPD)分光光度法和对苯二甲酸荧光光度法分别测定了降解过程中H2O2和羟基自由基(·OH)的变化,表明p-Bi2O2CO3/Vis光催化降解机理涉及到·OH历程。     

以废弃磷石膏为原料水热合成碳酸钙晶须的研究

以废弃磷石膏为钙源水热合成碳酸钙晶须,研究了不同反应前驱物和添加剂对碳酸钙样品晶形的影响,利用奥林巴斯显微镜和扫描电镜(SEM)观察晶体形貌,并用X衍射(XRD)和红外光谱(FTIR)对样品进行了表征。实验结果表明,采用柠檬酸钠为添加剂,在反应时间12 h,反应温度120℃,柠檬酸钠浓度2％的工艺条件下,可制得晶须长度约为50～120 μm、长径比为40～100∶1、大小相对均匀的文石型碳酸钙晶须。同时,实验还制得了形貌独特的稻草捆状和竹叶状碳酸钙晶体。     

Conversion of calcium sulphide to calcium carbonate during the process of recovery of elemental sulphur from gypsum waste

The production of elemental sulphur and calcium carbonate (CaCO₃) from gypsum waste can be achieved by thermally reducing the waste into calcium sulphide (CaS), which is then subjected to a direct aqueous carbonation step for the generation of hydrogen sulphide (H₂S) and CaCO₃. H₂S can subsequently be converted to elemental sulphur via the commercially available chemical catalytic Claus process. This study investigated the carbonation of CaS by examining both the solution chemistry of the process and the properties of the formed carbonated product. CaS was successfully converted into CaCO₃; however, the reaction yielded low-grade carbonate products (i.e. <90 mass% as CaCO₃) which comprised a mixture of two CaCO₃ polymorphs (calcite and vaterite), as well as trace minerals originating from the starting material. These products could replace the Sappi Enstra CaCO₃ (69 mass% CaCO₃), a by-product from the paper industry which is used in many full-scale AMD neutralisation plants but is becoming insufficient. The insight gained is now also being used to develop and optimize an indirect aqueous CaS carbonation process for the production of high-grade CaCO₃ (i.e. >99 mass% as CaCO₃) or precipitated calcium carbonate (PCC).     

Water geochemistry and dissolution rates of the karst-dominated Houzhai River basin,China

ABSTRACT

Houzhai (Guizhou Province, Southwest China) is a typical karstification area, with dolomite and limestone constituting the major rock types. The aim of this study was to utilize major element mass-balance and multivariate statistical methods to analyze the chemical composition of water in the Houzhai River catchment area with regard to seasonal variations in ion content, dissolution reactions, and rates. Data demonstrated that the Houzhai's hydrochemical composition is dominated by calcium (Ca²⁺), magnesium (Mg²⁺), bicarbonate (HCO₃^?), and sulfate (SO₄^2?) which predominantly originated from chemical weathering of carbonate rocks like limestone and dolomite. Carbonate weathering contributes 83% of the dissolved Ca²⁺. Sulfuric acid also plays an important role in rock weathering. Our analysis identified three principal sources of hydrochemical variation in the study area, including dolomite dissolution, limestone dissolution, and anthropogenic activities. In addition, the identified two main hydrochemical facies were characterized by the predominance of Ca-Mg-HCO₃ and Ca-Mg-HCO₃-SO₄. In terms of temporal variation, all of the examined parameters showed strong inter-annual and seasonal variations of concentration distribution, except pH levels and potassium and sodium (K⁺+Na⁺). The dissolution rate of carbonate was estimated using the concentration of Ca²⁺ and discharge rate, which constitutes a simple, practical, and innovative method. Compared with other research methods, our strategy was found to be simple, feasible, readily adaptable, and less demanding of data inputs.     

Effects of amine, amine salt and amide on the behaviour of carbon dioxide absorption into calcium hydroxide suspension to precipitate calcium carbonate

The amount of carbon dioxide （CO2） absorption and calcium ion （Ca^2＋） concentration besides the pH of aqueous solution were observed during the COz absorption to precipitate calcium carbonate （CaCO3） from calcium hydroxide （Ca（OH）2）. A reaction rate-limiting effect of an amount of CO2 absorption without any organic additives in the early stage of the precipitation was observed, which was attributed to an interruption effect of bicarbonate ion （HCO3） on the precipitation of CaCO3. The improvement for the reaction rate was achieved not only by amine additives but also by neutral additives such as ε-caprolactam or amine salt. When the hexamethylene diamine was dissolved in the solution, successive change of crystal forms of CaCO3 aragonite to calcite in aqueous suspensions, confirmed by Ca^2＋ concentration change and X-ray diffraction, was concluded that a local environment around the amine group in aqueous solution and an interaction of the diamine with precipitated CaCO3 particles were important factors for these reactions.     

The long-term stability of calcium arsenates: Implications for phase transformation and arsenic mobilization

It is well known that calcium arsenates may not be a good choice for arsenic removal and immobilization in hydrometallurgical practices. However, they are still produced at some plants in the world due to various reasons. Furthermore, calcium arsenates can also naturally precipitate under some specific environments. However, the transformation process of poorly crystalline calcium arsenates (PCCA) and the stability of these samples under atmospheric CO₂ are not yet well understood. This work investigated the transformation process of PCCA produced by using different neutralization reagents (CaO vs. NaOH) with various Ca/As molar ratios at pH?7–12 in the presence of atmospheric CO₂. After aging at room temperature for a period of time, for samples neutralized with NaOH and precipitated at pH?10 and 12, release of arsenic back into the liquid phase occurred. In contrast, for the samples precipitated at pH?8, the aqueous concentration of arsenic was observed to decrease. XRD, Raman, and SEM results suggested that the formation of various types of crystalline calcium carbonates and/or calcium arsenates controls the arsenic behavior. Moreover, the application of lime may enhance the stability of the generated PCCA. However, no matter what neutralization reagent is used, the stability of the generated PCCA is still of concern.     

悬浮液进样火焰原子吸收光谱法测定环境样品中钙、镁

将环境样品制成悬浮液，用空气／乙炔火焰原子吸收光谱法测定钙、镁、以三氯化镧、丙三醇和高氯酸为混合抗干扰剂，有效消除了环境样品中铅、磷、硫、硅等共存元素的干扰，其中丙三醇不仅是抗干扰剂，而且还起着稳定剂的作用，进一步简化了测定步骤，有效提高了分析速度。本文通过水溶液标准曲线校正，使测定更加方便。对测定结果与湿法消化法比较，具有较好的相关性。本法简便、快速、测定分析结果准确可靠。