Leaching characteristics of heavy metals during cement stabilization of fly ash from municipal solid waste incinerators

The leaching characteristics of heavy metals in products of cement stabilization of fly ash from a municipal solid waste incinerator were investigated in this paper. The stabilization of heavy metals such as Cd, Pb, Cu, and Zn in fly ash from such incinerators was examined through the national standard method in China based on the following factors: additive quantity of cement and Na₂S, curing time, and pH of leaching liquor. The results showed that as more additives were used, less heavy metals were leached except for Pb, which is sensitive to pH of the leachate, and the worse effect was observed for Cd. The mass ratio of cement to fly ash = 10% is the most appropriate parameter according to the national standard method. When the hydration of cement was basically finished, stabilization of heavy metals did not vary after curing for 1 d. The mixtures of cement and fly ash had excellent adaptability to environmental pH. The pH of leachate was maintained at 7 when pH of leaching liquor varied from 3 to 11.     

Fates and partitioning of heavy metals in municipal solid waste incineration process

The fate and partitioning of heavy metals (including Hg, Cd, Pb, Zn, As, Cr, Ni, and Cu) from MSW incinerators located in Taiwan were determined. Results of stack sampling indicate that most Hg and As (more than 80%) exists in the gas phase while other metals partition differently among bottom ash, fly ash, and flue gases. Removal efficiencies of existing air pollution control devices for Hg and As are lower (about 70%) than other metals. Bottom ash contains higher concentration of Cd compared with European incinerators. In addition, strong enrichment of Cd on fly ash particles is observed.     

Calcium carbonate waste from an integrated pulp and paper mill as a potential liming agent

Calcium carbonate is used in large amounts in the pulp and paper industry as a paper filler. When it is manufactured, the calcium carbonate waste is purged from the process. Here we demonstrate that, due to the elevated calcium concentration of 168.5 g kg⁻¹ dry weight (dw), alkaline pH of 12.6 and neutralizing (liming) effect value of 42.4% expressed as Ca equivalents, this waste is a potential liming agent and a pH buffer. The heavy metal concentrations in the waste were lower than the new Finnish limit values for fertilizers used in agriculture, as well as for a material, e.g. ash, used as an earth construction agent. These limit values came into force in March 2007 and in June 2006, respectively.     

广东某垃圾焚烧炉周边空气颗粒物中金属浓度特征及源解析研究

以广东某垃圾焚烧炉为研究对象,应用富集因子法、主成分分析法对其周边环境空气中金属(Fe、Al、Mg、Cu、Zn、Mn、Ba、Pb、Cr、Ni、Bi和Cd)含量及来源进行分析.结果如下:研究区域环境空气中各金属含量(各点均值)(ng·m-3)为:Fe(1092—3487)Al(939—3126)Mg(716—1339)Cu(63.4—995)Zn(227—427)Mn(162—291.1)Ba(61.4—372)Pb(21.9—41.8)Cr(12.3—25.7)Ni(5.70—15.5)Bi(0.70—1.22)Cd(0.42—0.82).相关分析和主成分分析发现,研究区域Fe与Ni、Cr、Mn、Ba主要来自于焚烧炉释放,Zn、Cd、Pb、Bi和Cu则来自于研究区域周边的交通污染源,而Al和Mg则主要来自于地壳或土壤背景值.     

Effects of sulfur on variations in the chemical speciation of heavy metals from fly ash glass

● A higher sulfur content reduced the curing rate of Cr in glass. ● Depolymerization increased the amounts of heavy metals in the carbonate bound state. ● Reducing the CaO/SiO₂ ratio increased the proportion of stable heavy metals. This work designed a new CaO-Al₂O₃-SiO₂-SO₃ glass for the immobilization of multiple heavy metals found in dechlorinated fly ash having high amounts of calcium and sulfur. Increasing the (CaO + SO₃)/SiO₂ mass ratio (M(CS/S)) from 0.28 to 0.85 was found to lower the proportions of Mn, Ni and Zn in an unstable state, while an M(CS/S) ratio of 0.51 gave the lowest proportions of unstable Cr and Pb. Decreasing the degree of polymerization of the glassy network increased the proportions of Mn, Cr, Ni, Pb and Zn in the carbonate bound state. The leaching out of metals in this state was the primary cause of degradation of Q³ structural units in the glassy network. The amount of Mn in the iron-manganese oxide bound state was increased by increasing the number of Q² units in the silicate network. Decreasing the CaO/SiO₂ mass ratio (M(C/S)) raised the proportions of Mn, Ni and Zn in the unstable state. An M(C/S) value of 0.43 lowered the proportions of unstable Cr and Pb. A principal components analysis determined that the leaching of toxic heavy metals from the glass was primarily related to the proportions of these metals in the unstable state while there were no evident correlations between leaching and the proportions in stable states.     

Evaluation of dilute hydrochloric acid and acid ammonium oxalate as extractants for some heavy metals from Nile River sediments

The suitability of a 0.5 M HCl solution for extraction of Fe, Mn, Cd, Co, Cu, Pb, and Zn from Nile River sediments was evaluated by comparing its effectiveness with that of conventional acid ammonium oxalate (Tamm's solution) and aqua regia extraction solutions. The present study has shown that although the extraction data indicate that both 0.5 M HCl and acid ammonium oxalate solutions are able to extract heavy metals simultaneously from the adsorbed, organic, and precipitated phases of Nile sediments, the 0.5 M HCl solution is preferred. It provides a rapid, reliable, and inexpensive method of measuring environmentally mobile metal concentrations in the aquatic sediments. From an analytical chemistry point of view, the 0.5 M HCl extracts do not clog the atomizer of the spectrophotometer. Extraction with dilute HCl solution obviates the need to use chemicals, some of which are toxic or not available readily as a high-purity grade. A standard extraction method should be relatively simple, to conduct a routine analysis of large numbers of sediment samples, yet at the same time it should provide sufficient information for assessment of the environmental impact of particulate metals. Therefore, extraction with 0.5 M HCl solution is very suitable for heavy-metal pollution monitoring in the Nile River     

龙塘镇电子垃圾拆解区土壤和河流底泥重金属赋存形态及生态风险

龙塘镇是珠三角电子垃圾拆解区之一,采用AAS方法对该地土壤和河流底泥沉积物中5种重金属(Cd、Cr、Cu、Zn和Pb)含量进行测定分析,结果显示周围农田土壤中Cd含量是《国家土壤质量标准》二级标准的3倍左右,是广东省土壤背景值的20倍左右;拆解区土壤Cd超标最为严重,最高达5.67倍,超过广东省土壤背景值达36.17倍;拆解区下游0—1500 m河流底泥中Cd、Cr、Cu、Zn和Pb含量大幅增加且部分金属超标,Cd在0—40 cm深度内含量总体逐渐降低,仍远超背景值,Cu含量采样深度内递减规律最显著且在0—10 cm内含量超标,Cr、Zn和Pb除部分点位在表层积累较多外,其余与背景值相差不大且未超标.采用BCR(the Community Bureau of Reference)法提取重金属不同形态可知,底泥中Cd主要以弱酸溶态和可还原态为主,Cu主要以可氧化态存在,Cr主要以残渣态存在,而Zn和Pb则以可还原态为主;其中Cd的可提取态比例较高(60%),容易释放出来形成"二次污染".潜在生态风险结果表明,河流底泥中Cd生态危害程度属于极强(Ei320);其他金属Cr、Cu、Zn和Pb危害风险程度属于轻微(Ei40);金属Cd对整个RI值贡献最大(88%),应重点加强对Cd污染的防控.     

Comparative study of the age and location dependence of some heavy metals in human hair from two Nigerian cities

The concentration of some heavy metals (lead, zinc and copper) were determined in the scalp hair of children (1–15 year) and active adults (16–40 year) in two Nigerian cities. The levels of zinc were found to be higher in children than in the adult population. There was a significant difference (P?=?0.05) between the two age groups. The levels of copper were all within the same range for the two age groups and independent of location. The levels of lead were generally higher in adults than in children. However, there was no significant difference (P?=?0.05) in the average concentrations of lead between the children and adult populations of the two cities. The regression analysis indicated a strong correlation (r?=?0.86) between zinc and copper.     

粤西三座重要供水水库沉积物营养盐负荷与重金属污染特征

为揭示粤西3座供水水库（高州水库、鹤地水库、大水桥水库）沉积物营养盐负荷及重金属污染特征,于2008年6月在各水库大坝前湖泊区采集柱状沉积物,运用SMT法、碱性过硫酸钾消解法、烧失法和ICP-MS法分别测定其柱状沉积物中氮磷营养盐、有机质和7种重金属（Cu、Pb、Zn、Cd、Ni、Cr与Hg）的含量,并采用潜在生态风险指数法对表层重金属污染的潜在生态风险进行评价,同时通过相关性分析重金属的可能来源。结果表明：3座水库沉积物总氮质量分数为1.13~3.37 mg·g-1,有机质为11.83~20.37 mg·g-1,其表层总氮、有机质的质量分数大小顺序为高州水库〉大水桥水库〉鹤地水库,总磷的质量浓度在0.22~0.77 mg·g-1之间,其表层总磷质量分数大小顺序为高州水库〉鹤地水库〉大水桥水库,在垂直剖面上,总氮、总磷与有机质的质量分数在16 cm至表层沉积物垂直断面显著高于其他断面,表明近些年来水库内源营养盐负荷逐渐加重。重金属质量分数平均值均高于广东省土壤环境背景值,总体呈现随深度增加而降低的趋势,但3座水库间重金属质量分数差异较大,其中鹤地和高州水库的Zn和Pb污染相对严重（质量分数分别为Zn：353.15、693.35 mg·kg-1;Pb：74.51、127.91 mg·kg-1）,大水桥水库的Cr和Ni污染相对严重（质量分数分别为Cr：238.69 mg·kg-1;Ni：251.06 mg·kg-1）。潜在生态风险评价表明,3座水库Cd和Hg具有高的生态危害,应引起重视,其他重金属则处于轻微的生态危害等级。同时沉积物高有机质的质量浓度经矿化分解可能加剧水体重金属生态危害。根据相关性分析和其他相关资料可知,粤西农业区大量化肥农药面源污染汇入造成水库初级生产力提高并最终沉降可能是沉积物营养盐、有机质与重金属的主要来源。     

成都市河流表层沉积物重金属污染及潜在生态风险评价

根据流经成都市内的三条河流（府河、南河、沙河）表层沉积物重金属数据，采用Hakanson潜在生态危害指数法对重金属的潜在生态风险进行了评价。结果表明（1）重金属潜在的生态危害因子（Er^i）说明大多属于轻微生态危害范畴，产牛生态危害的主要重金属是Hg、Cd，Cu、Pb次之，As影响最小；（2）多种重金属的生态系统的潜在生态风险指数（RI）表明河流重金属污染属于轻微生态危害和接近中等生态危害，其受危害程度由强至弱的次序为：府河，南河，沙河。