酸淋洗土壤中重金屬之研究

Acid Leaching of Heavy Metals from Contaminated Soils

陳武清(Wu C. Chen)

指導教授 ： 林勝雄

元智大學/工程學院/化學工程與材料科學學系/碩士(1998年)

摘要

重金屬污染時有所聞，尤其是土壤所受到的重金屬污染最為嚴重，因為土壤成份較複雜，要去除重金屬頗不易，本論文即針對去除土壤中的重金屬為目的。所選用的化學藥劑為三種強酸，探討何者去除重金屬效果高及對土壤性質改變最小。
在批次實驗中發現，三種強酸中以鹽酸去除鎘的效果最好，硝酸與硫酸稍差一點，且硫酸會將土壤中的有機成份萃出，故不建議用硫酸。在恆溫去除實驗方面，Freundlich比Langmuir適合本去除現象的等溫平衡關係。在質傳模式的探討上，以簡單的平方推動力模式，即可合適地表達本實驗之質傳現象。
連續淋洗實驗是將酸溶液流經固定的土壤床，目的是測試此實驗的效能如何，以探討其實用性。在理論方面，Logistic、修正之Wheeler、Gompertz、Richards、Weibull等方程式皆可適切模擬淋洗之去除貫穿曲線；而Logistic、修正之Wheeler與Gompertz方程式更可進一步成功的預測不同通量的去除貫穿曲線。
現地連續淋洗實驗，是以桃園蘆竹鄉新興村中褔社區的鎘污染土壤為樣品，以長30公分寬30公分的管柱填充污染土壤進行酸洗，結果仍是以鹽酸溶液效果最佳；土壤淋洗後，將土壤以石灰中和酸性，試種蔬菜，結果其生長狀況相當良好；另外，流經土壤的淋洗液以氫氧化鈉調至pH 10以上，即有氫氧化鎘與氫氧化鉛沈澱產生，將上層澄清液排放後，沈澱物以水泥固化。這些步驟串在一起即可為現場處理流程的參考，且為土壤復育依據。

關鍵字

酸淋洗土壤 ； 重金屬污染土壤 ； 土壤復育 ； 貫穿曲線 ； 重金屬去除 ； 鎘去除 ； 土壤 ； 中輻社區污染土壤

並列摘要

Metal contamination is a prevalent and wide-spread problem in Taiwan and the soil contamination is known to be the most serious one. Removal of heavy metals from contaminated soil is not easy due to the complex metrical structure and intricate interactions of heavy metals with various inorganic or organic components present in the soil. The purpose of this research is to investigate the heavy metal leaching by three strong acids (i.e. hydrochloric, sulfuric and nitric acids). Experiments were conducted to evaluate the effectiveness of each acid as a leaching agent and to assess the characteristic changes of soil caused by the acid leaching process.
The results of batch tests revealed that among the three strong acids, hydrochloric acid is more efficient than the other two in removing cadmium from contaminated soil. Test results also showed that significant amount of organic (nutrient) components will be extracted along with cadmium by sulfuric acid and it is not acceptable as leaching agent. The equilibrium test data allowed establishment of the desorption isotherm. The empirical Freundlich model was found to represent the observed data better than the Langmuir model. In the mass transfer aspect, the model based on the squared-driving principle was seen to describe well the overall mass transfer process.
Continuous tests of heavy metal leaching were also carried out in a fixed bed soil column to determine effects of operating variables, including acid concentration and flow rate, leaching time, heavy metal concentration, amount of soil, etc. Various empirical or semi-empirical equations, like logistic, Wheeler, Gompertz, Richard and Weibull model, were employed to represent the leaching breakthrough curves. Goodness of fit of these models to the observed data was evaluated.
A native, contaminated soil was collected from the field located in Chung Fu area, Lu Tsu, Taoyuan County. The soil sample was leaching tested in a pilot plant square column of 30 cm (W) x 30 cm (L) x 100 cm (H) using hydrochloric acid. The soil column after leaching test was neutralized by slacked lime and blended with varying amounts of chicken mature composite. The treated soil was seeded and the vegetables were found to grow quite well. The leaching effluent from the column tests containing cadmium and lead was adjusted by sodium hydroxide to over pH 10. Cadmium and lead hydroxides quickly settled out of the aqueous solution with only trace amounts of heavy metals leaving behind. The metal hydroxides were finally solidified using regular Portland cement mixed with solidifying agent for easy deposal.

並列關鍵字

Acid Leaching Soils ； Heavy Metals ； Breakthrough Curve ； Removal Heavy Metals ； Removal Cadmium ； Soils

參考文獻

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