简介概要

Na2CO3-CO2-H2O体系处理铬渣的热力学分析

来源期刊:中南大学学报(自然科学版)2011年第5期

论文作者:刘伟 李斌 周秋生 齐天贵 彭志宏 刘桂华 李小斌

文章页码:1209 - 1214

关键词:铬渣;Cr(Ⅵ);浸出;热力学

Key words:chromite ore processing residue (COPR); Cr(Ⅵ); leaching; thermodynamics

摘    要:采用Na2CO3-CO2-H2O体系处理铬渣,分析该体系的反应热力学,并通过实验研究不同浸出剂对铬渣中 Cr(Ⅵ)浸出的影响。研究结果表明:在75 ℃,当6.6<pH<10.8且c(CO32-)>1.55×10-6 mol/L时,体系处于碳酸钙的稳定区,铬酸钙、水榴石、水铝钙石及钙铁石可被分解而释放出其中的Cr(Ⅵ),而水滑石难以被分解;在温度为80 ℃,碳酸钠质量浓度为120 g/L,液固比为15,CO2体积分数为5%,时间为24 h的条件下处理铬渣,得到的渣经湿磨后再用此体系二次浸出,最终铬渣中Cr(Ⅵ)的质量分数降至0.13%,Cr(Ⅵ)的浸出率达到85%;毒性实验浸出液中Cr(Ⅵ)和总Cr质量浓度分别为1.21 mg/L和1.51 mg/L,均远低于HJ/T 301—2007中规定的限值,符合一般工业固体废物填埋的标准;含Cr(Ⅵ)的主要物相钙铁石、水铝钙石的质量分数明显降低且没有铬酸钙生成,这与热力学分析结果基本一致。

Abstract: A new system of Na2CO3-CO2-H2O was employed to leach Cr(Ⅵ) in the chromite ore processing residue (COPR). The thermodynamic analysis was carried out and the effect of various leaching reagents on Cr(Ⅵ) leaching was studied. The results show that the system is in the stability region of CaCO3 at 75 ℃ with pH in 6.6-10.8 and the CO32- concentration above 1.55×10-6 mol/L, and thus CaCrO4, hydrogarnet, hydrocalumite and brownmillerite may be decomposed, resulting in the release of Cr(Ⅵ), while hydrotalcite can hardly be decomposed. The content of Cr(Ⅵ) in COPR treated by Na2CO3-CO2-H2O leaching followed by wet-grinding and then leaching, and the leaching efficiency of Cr(Ⅵ) in COPR can reach 0.13% and 85% respectively under the optimal conditions of 80 ℃, liquid-solid ratio of 15, CO2 concentration in the mixture of CO2 and air of 5%, Na2CO3 mass concentration of 120 g/L and leaching time of 24 h. The Cr(Ⅵ) and total Cr mass concentrations in the leachate of toxicity characteristic leaching procedure of the COPR treated under the above optimal conditions are 1.21 mg/L and 1.51 mg/L respectively, far below the regulatory limit and meeting the landfill standard for common industrial solid waste in HJ/T 301—2007. The contents of brownmillerite and hydrocalumite regarded as the main Cr(Ⅵ)-bearing phases reduce obviously and there are no apparent diffraction peaks of CaCrO4, approximately in agreement with the thermodynamic calculation.



详情信息展示

Na2CO3-CO2-H2O体系处理铬渣的热力学分析

刘伟,李斌,周秋生,齐天贵,彭志宏,刘桂华,李小斌

 (中南大学 冶金科学与工程学院,湖南 长沙,410083)

摘要:采用Na2CO3-CO2-H2O体系处理铬渣,分析该体系的反应热力学,并通过实验研究不同浸出剂对铬渣中 Cr(Ⅵ)浸出的影响。研究结果表明:在75 ℃,当6.6<pH<10.8且c(CO32-)>1.55×10-6 mol/L时,体系处于碳酸钙的稳定区,铬酸钙、水榴石、水铝钙石及钙铁石可被分解而释放出其中的Cr(Ⅵ),而水滑石难以被分解;在温度为80 ℃,碳酸钠质量浓度为120 g/L,液固比为15,CO2体积分数为5%,时间为24 h的条件下处理铬渣,得到的渣经湿磨后再用此体系二次浸出,最终铬渣中Cr(Ⅵ)的质量分数降至0.13%,Cr(Ⅵ)的浸出率达到85%;毒性实验浸出液中Cr(Ⅵ)和总Cr质量浓度分别为1.21 mg/L和1.51 mg/L,均远低于HJ/T 301—2007中规定的限值,符合一般工业固体废物填埋的标准;含Cr(Ⅵ)的主要物相钙铁石、水铝钙石的质量分数明显降低且没有铬酸钙生成,这与热力学分析结果基本一致。

关键词:铬渣;Cr(Ⅵ);浸出;热力学

中图分类号:X705           文献标志码:A         文章编号:1672-7207(2011)05-1209-06

Thermodynamic analysis of chromite ore processing residue treatment in Na2CO3-CO2-H2O system

LIU Wei, LI Bin, ZHOU Qiu-sheng, QI Tian-gui, PENG Zhi-hong, LIU Gui-hua, LI Xiao-bin

(School of Metallurgical Science and Engineering, Central South University, Changsha 410083, China)

Abstract: A new system of Na2CO3-CO2-H2O was employed to leach Cr(Ⅵ) in the chromite ore processing residue (COPR). The thermodynamic analysis was carried out and the effect of various leaching reagents on Cr(Ⅵ) leaching was studied. The results show that the system is in the stability region of CaCO3 at 75 ℃ with pH in 6.6-10.8 and the CO32- concentration above 1.55×10-6 mol/L, and thus CaCrO4, hydrogarnet, hydrocalumite and brownmillerite may be decomposed, resulting in the release of Cr(Ⅵ), while hydrotalcite can hardly be decomposed. The content of Cr(Ⅵ) in COPR treated by Na2CO3-CO2-H2O leaching followed by wet-grinding and then leaching, and the leaching efficiency of Cr(Ⅵ) in COPR can reach 0.13% and 85% respectively under the optimal conditions of 80 ℃, liquid-solid ratio of 15, CO2 concentration in the mixture of CO2 and air of 5%, Na2CO3 mass concentration of 120 g/L and leaching time of 24 h. The Cr(Ⅵ) and total Cr mass concentrations in the leachate of toxicity characteristic leaching procedure of the COPR treated under the above optimal conditions are 1.21 mg/L and 1.51 mg/L respectively, far below the regulatory limit and meeting the landfill standard for common industrial solid waste in HJ/T 301—2007. The contents of brownmillerite and hydrocalumite regarded as the main Cr(Ⅵ)-bearing phases reduce obviously and there are no apparent diffraction peaks of CaCrO4, approximately in agreement with the thermodynamic calculation.

Key words: chromite ore processing residue (COPR); Cr(Ⅵ); leaching; thermodynamics

铬渣(COPR)是铬铁矿经高温焙烧、用水浸取铬酸钠后得到的废渣。传统有钙焙烧工艺产生的铬渣含有0.5%~2.0%(质量分数)的Cr(Ⅵ),被列为危险废物[1]。目前,铬渣处理仍然以堆存为主,而铬渣堆存有2个方面的问题:一是铬渣中Cr(Ⅵ)随雨水源源不断地浸出;二是铬渣的体积膨胀无法控制[2]。因此,对铬渣进行解毒与综合利用势在必行。将铬渣中的Cr(Ⅵ)转移至液相,主要有水化法[3]、酸溶法[4]和碱溶法[4]。水化法是用水作浸出剂,利用铁铝酸钙等的水化特性,将铬渣中的水溶性和少部分酸溶性Cr(Ⅵ)转移到溶液中。由于Cr(Ⅵ)浸出不彻底,Geelhoed等[5]否定了用此法来解毒铬渣。而酸溶法是用硫酸等强酸破坏铬渣中含Cr(Ⅵ)物质的结构,从而将渣中Cr(Ⅵ)转移到液相中。由于铬渣具有很强的pH缓冲能力,将其pH由12.0调至7.5所需酸量较大,导致其解毒成本较高[5]。考虑到铬渣中含有大量的碱性物质,以碱性体系处理铬渣应该更加合理。景学森等[6]对铬渣中Cr(Ⅵ)在不同盐溶液中的浸出效果进行了比较,发现Na2CO3溶液的浸出效果最好,Cr(Ⅵ)浸出率可达77%;陈振林等[7]用CO2处理铬渣,在常温常压下于水中处理3 h,渣中Cr(Ⅵ)的浸出率也可达65%。目前,单独用CO2或Na2CO3处理铬渣均无法实现铬渣解毒,且其解毒机理不清楚。为此,本文作者对采用Na2CO3-CO2-H2O体系处理铬渣进行热力学计算和分析,并在此基础上进行实验研究,以便寻找一种强化铬渣中含Cr(Ⅵ)的钙镁复杂化合物分解的方法,开发铬渣解毒新技术。

1  实验

1.1  实验原料

实验所用铬渣取自某铬渣堆场,其主要化学成分(质量分数)见表1。将铬渣在50 ℃时烘干12 h,然后,磨细至过75 μm筛作为实验原料。所用碳酸钠为化学纯,二氧化碳为工业纯。

表1  铬渣的主要化学组成

       Table 1  Chemical composition of COPR      %

1.2  实验步骤

将一定量铬渣置于直径×长度为35 mm×315 mm的玻璃管中,按液固比为15加入设定浓度的碳酸钠溶液(浓度以Na2O计),混合均匀后在恒温水浴槽中保温一段时间,达到预定温度后,从溶液底部通入二氧化碳与空气的混合气体(CO2体积分数为5%)并开始反应计时。在反应过程中气体流量维持在0.1 m3/h左右,以保证反应物料的搅拌效果不受影响。反应结束后,进行固液分离并测定滤液的pH,将处理后的铬渣充分洗涤后烘干、称质量,最后分析渣中Cr(Ⅵ)的含量并计算铬渣中Cr(Ⅵ)的浸出率。

1.3  分析方法

渣中Cr(Ⅵ)的含量依据GB 5085.3—2007《危险废物鉴别标准:浸出毒性鉴别》中《附录T:固体废物—六价铬分析的样品前处理—碱消解法》和GB/T 15555.4—1995《固体废物:六价铬的测定—二苯碳酰二肼分光光度法》进行测定;溶液的pH用酸度计(PHS-25C Precision)测定;渣的物相组成采用X线衍射仪(D/MAX-RA)进行分析。

2  结果与讨论

2.1  热力学计算与分析

2.1.1  铬渣中Cr(Ⅵ)的存在形式

铬渣的物相组成极其复杂,国内外学者综合运用XRD(X线衍射),FT-IR(红外),SEM-EDX(扫描电镜-能谱)和XRF(X线荧光)对铬渣中Cr(Ⅵ)的存在形式进行了研究[8-11],主要结果见表2。物相中四水铬酸钠呈水溶性,铬酸钙呈微溶性,而其他几种物质都是呈难溶性。

2.1.2  热力学参数及计算

由表2可知:钙钒石中Cr(Ⅵ)的含量极少。故在此未对其进行热力学分析,而主要对水榴石、水铝钙石、水滑石及钙铁石在Na2CO3-CO2-H2O体系中的反应行为进行热力学分析。

有色金属在线官网  |   会议  |   在线投稿  |   购买纸书  |   科技图书馆

中南大学出版社 主办 版权声明   电话:0731-88830515 88830516   传真:0731-88710482   Email:administrator@cnnmol.com

互联网出版许可证:新出网证(湘)字005号   湘ICP备09001153号