几种含铬钙矾石的合成试验研究

Experiments on the synthesis of chromium-containing ettringites

通过室内人工合成的几种含铬钙矾石的试验发现,Cr(Ⅲ)、Cr2O2-7、CrO2-4等均可进入钙矾石晶格而被固化。Cr2O2-7是以CrO2-4的形式进入钙矾石晶格的。试验表明,在缺乏SO2-4供应充分时,CrO2-4很容易替代SO2-4进入钙矾石晶格,形成铬酸钙矾石;但在SO2-4供应充分时,CrO2-4基本上不能进入钙矾石晶格。因此为了有效地固化CrO2-4,必须选择无石膏的水泥类型。在无铝离子时,Cr(Ⅲ)在高浓度的NaOH溶液中可替代Al与SO2-4或与CrO2-4结合分别形成Cr(Ⅲ)-硫酸钙矾石或双铬钙矾石。但在Ca(OH)2中等碱性溶液中,Cr(Ⅲ)主要以Cr(OH)3的形式存在,其溶解度很小,Cr(Ⅲ)基本上不能替代Al与SO2-4或与CrO2-4结合形成钙矾石。尽管如此,双铬钙矾石的成功合成对同时含有Cr(Ⅲ)和CrO2-4的废水进行S/S处理提供了新的思路。

The synthetic chromium-containing ettringites experiments indicates that Cr(Ⅲ),Cr_2O^(2-)_7 and CrO^(2-)_4 can be solidified in ettringites.Cr_2O^(2-)_7 enters into ettringites as the form of CrO^(2-)_4 can easily incorporate with calcium ions and aluminate ions to form chromate ettringites when the solution is free of sulfate or when sulfate is in short supply.But when sulfate is abundant in the solution,chromate has little chance to enter into the ettringites' lattice due to elimination series.In order to solidified chromate effectively,cement with little gypsum or other sulfate-containing additives can only be considered.When the solution is avoid of aluminum,Cr(Ⅲ) can substitute for aluminum and incorporate with sulfate or with chromate to form Cr(Ⅲ)-sulfate ettringites or double chromium ettringite which contain both Cr(Ⅲ) and Cr(Ⅵ) in high alkaline solution(high concentration of sodium hydroxide).But in limewater which is medium alkaline solution,Cr(Ⅲ) precipitated as Cr(OH)_3.Since the solubility of Cr(OH)_3 is very little in medium alkaline solution,Cr(Ⅲ) cannot substitute for aluminum to form any ettringites.However the successful synthesis of the double chromium ettringite provides an innovative treatment of the wastewater which contains both Cr(Ⅲ) and Cr(Ⅵ).