弗氏盐法废水除氯产物资源化及二次利用进展

Progress on resource utilization and second utilization of chloride removal products from Friedel's salt precipitation method

废水中高浓度氯离子不仅会腐蚀工业设备,还易污染水环境。目前,已报道了一系列去除废水中氯离子的技术,如膜分离或浓缩、蒸发结晶、化学沉淀、吸附、离子交换、电解、氧化和溶剂萃取等。化学沉淀法在设备投资和可操作性等方面具有较大的优势,其中,相对于基于银、铜或铋等除氯方法,弗氏盐沉淀除氯法因所用原料来源广、价格低而得到广泛研究。但弗氏盐沉淀除氯后会产生大量的化学污泥,这些污泥主要含有弗雷德盐(3CaO·Al_(2)O_(3)·CaCl_(2)·10H_(2)O)、加藤石[Ca_(3)Al_(2)(OH)_(12)]和氢氧化钙等,成分复杂,循环再生难。为使弗氏盐沉淀除氯法能够推广应用,对其除氯产物,特别是其中的弗雷德盐进行资源化再利用至关重要。本工作在介绍弗雷德盐成分结构特性的基础上,通过比较弗雷德盐不同制备方法,突出弗氏盐沉淀法(如超高石灰铝法和钙铝石法)既能去除氯离子又能得到弗雷德盐的优势。根据弗雷德盐含铝和钙成分和层状双金属氢氧化物结构特性,可进行有效的资源化利用,包括去除各类重金属阳离子(如Cu^(2+),Cd^(2+),Co^(2+),Zn^(2+),Pb^(2+))和含氧阴离子[如Sb(OH)_(6)^(-),AsO_(4)^(3-),SeO_(4)^(2-),CrO_(4)^(2-)],并制备聚合氯化铝混凝剂、作为污泥脱水调理剂等,这些用途都具有广阔的应用前景,为弗氏盐沉淀除氯法的进一步发展提供借鉴和探索方向。

The high concentration of Cl^(-)in wastewater can seriously corrode industrial equipment,and also pollute the water environment.A series of technologies for removing Cl^(-)from wastewater have been reported,such as membrane separation,concentration,evaporation crystallization,chemical precipitation,adsorption,ion exchange,electrolysis,oxidation,and solvent extraction.Among them,chemical precipitation has significant advantages in equipment investment and operability,Friedel's salt precipitation method of Cl^(-)removal has been intensively studied because of the wide source and low price of raw materials,compared with other methods using silver,copper,or bismuth.After the Cl^(-)removal,a large quantity of chemical sludge is produced,which mainly contains Friedel's salt(3CaO·Al_(2)O_(3)·CaCl_(2)·10H_(2)O),katoite[Ca_(3)Al_(2)(OH)_(12)],and calcium hydroxide,etc.Due to the complex components and the tight binding of Cl^(-)in the interlayer spacing of Friedel's salt,the resultant sludge is difficult to recycle.To promote the application of Friedel's salt precipitation method,it is very important to utilize its Cl^(-)removal products,especially Friedel's salt,as a resource.Based on the introduction of the compositional and structural characteristics of Friedel's salt,this work highlights the advantages of Friedel's salt precipitation method,which cannot only remove Cl^(-),but also obtain Friedel's salt,by comparing other preparation methods.According to the aluminum and calcium components of Friedel's salt and its layered bimetallic hydroxide structure,effective resource utilization can be carried out,including the removal of various heavy metal cations(i.e.,Cu^(2+),Cd^(2+),Co^(2+),Zn^(2+),and Pb^(2+))and oxygenated anion complexes[i.e.,Sb(OH)6-,AsO_(4)^(3-),SeO_(4)^(2-),and CrO_(4)^(2-)],and the preparation of polyaluminum chloride coagulants and as sludge dewatering regulators,etc.These uses have broad application prospects,providing reference and exploration direction for the further development of Friedel's salt precipitation method.Key learning points:(1)The bottleneck encountered by Friedel's salt precipitation method and the importance of resource reuse of its chloride removal product of Friedel's salt are elaborated.(2)The composition,structural characteristics,and differences of Friedel's salt in the chloride removal products are introduced,as well as the advantages of the methods of chloride removal and obtaining Friedel's salts.(3)The application progress of Friedel's salt in the fields such as the removal of heavy metal ions,construction of polyaluminum chloride coagulants,and sludge dewatering regulators is summarized.(4)The challenges and future development prospects of Friedel's salt in application are proposed,providing a reference for the promotion and application of Friedel's salt precipitation method.