Sitko Rafał, Zawisza Beata, Krzykawski Tomasz, Malicka Ewa
Institute of Chemistry, Silesian University, Katowice, Poland.
Talanta. 2009 Jan 15;77(3):1105-10. doi: 10.1016/j.talanta.2008.08.019. Epub 2008 Aug 30.
Determination of chemical composition of siderite (Fe, Me)CO(3) (where Me=Mg, Ca, Mn) present in siderite concretion is developed. An accurate and precise determination of Mg, Ca, Mn and Fe in siderite required complete separation of this mineral from other materials, e.g. calcite, quartz. For this purpose, selective dissolution in acetic acid (HAc) was applied. HAc concentration from 0.1 to 1 mol L(-1) and extraction time from 0.5 to 8h were investigated. In each step of investigation of selective dissolution, the X-ray diffraction measurements (XRD) of the residues was performed and also calcium (complexometric titration) and iron (XRF) in solution were determined. HAc of concentration 0.25 mol L(-1) and extraction time of 2h was adopted for siderite separation because in these conditions the siderite was not dissolved and, simultaneously, calcite was completely dissolved. In the next step, the nondissolved sample was digested in hydrochloric acid. The solution of the separated siderite was pipetted onto membrane filter and Mg, Ca, Mn and Fe were determined by wavelength-dispersive X-ray fluorescence (WDXRF) spectrometry. The calibration was performed using 11 certified reference materials of iron ores. Matrix effects were corrected using empirical coefficient model for intermediate-thickness samples.
开展了菱铁矿结核中菱铁矿（Fe，Me）CO₃（其中Me = Mg、Ca、Mn）化学成分的测定。准确精确地测定菱铁矿中的Mg、Ca、Mn和Fe需要将该矿物与其他物质（如方解石、石英）完全分离。为此，采用了在乙酸（HAc）中选择性溶解的方法。研究了0.1至1 mol L⁻¹的HAc浓度以及0.5至8小时的萃取时间。在选择性溶解研究的每个步骤中，对残渣进行了X射线衍射测量（XRD），并测定了溶液中的钙（络合滴定法）和铁（XRF）。采用0.25 mol L⁻¹的HAc浓度和2小时的萃取时间进行菱铁矿分离，因为在这些条件下菱铁矿未溶解，同时方解石完全溶解。下一步，将未溶解的样品用盐酸消化。将分离出的菱铁矿溶液移液至膜滤器上，并用波长色散X射线荧光（WDXRF）光谱法测定Mg、Ca、Mn和Fe。使用11种认证铁矿石参考物质进行校准。采用经验系数模型对中等厚度样品的基体效应进行校正。
