Effect of biochar on migration of heavy metals in mining soil under leaching conditions

doi:10.16085/j.issn.1000-6613.2019-0726

Abstract

Abstract:

Biochar was prepared from corn straw at 450℃, and the biochar was applied to the heavy metal contaminated soil in mining area with 5% carbon/soil dry weight ratio. The effects of biochar addition on the pH of soil leachate, vertical migration behavior and cumulative release of heavy metals were analyzed by soil column leaching test in laboratory. The results showed that the pH of soil leaching solution in biochar added soil was significantly higher than that of the control treatment, indicating that adding biochar had advantages in alleviating soil acidity. Compared with the control, the addition of biochar reduced the risk of heavy metal migration to the lower layer. The vertical migration of Pb, Cu, Zn and Mn in the soil column after leaching decreased by 65.93%, 50.95%, 49.29% and 30.95%, respectively. The order of inhibition of vertical migration of heavy metals by biochar was Pb＞Cu＞Zn＞Mn, and biochar had the best passivation effect on Pb. With the increase of leaching solution volume, the leaching cumulative releases of Pb, Cu, Zn and Mn in soil appeared to be consisted of two phases involving the initial rapid process followed by a slow continuous process. The cumulative release of the four heavy metals was Pb＞Mn＞Zn＞Cu, and the cumulative release of heavy metals was significantly reduced by adding biochar. The release processes of heavy metals from soil were fitted with mathematical equations. The Elovich equation could better describe the release process of heavy metals, which indicated that the mechanism of leaching and releasing process of these four heavy metals in soil was not a single reaction process, but a complex reaction process with large change of activation energy. After adding biochar, the b value of all heavy metals was lower than that of the control group. The migration rate of heavy metals decreased with the addition of biochar, indicating that the adding biochar could improve the adsorption capacity of soil to heavy metal ions, reduce the migration of heavy metals caused by soil leaching, and could realize the remediation of the soil in heavy metal complex contaminated mining areas.

Key words: mining soil, heavy metal, biochar, leaching, migration, release characteristic

摘要：

以玉米秸秆为原料在450℃下制备生物炭，将生物炭按5%的炭土比例施入矿区重金属污染土壤中。通过室内土柱淋溶试验，分析加入生物炭对土壤淋出液pH、重金属纵向迁移行为及重金属累积释放量的影响。结果表明：加入生物炭处理后土壤淋出液的pH显著高于对照处理，说明生物炭可以在一定程度上缓解土壤的酸性。与对照相比，添加生物炭降低了重金属向下层土壤迁移的风险，淋溶后土柱中Pb、Cu、Zn和Mn的纵向迁移量分别降低了65.93%、50.95%、49.29%和30.95%，生物炭对土壤中重金属纵向迁移抑制的顺序为Pb>Cu>Zn>Mn，生物炭对Pb的钝化效果最好。随着淋溶液体积的增加，Pb、Cu、Zn和Mn这4种重金属的淋溶累积释放量总体上呈现出前期快速溶出和后期缓慢溶出两个明显的阶段。4种重金属的累积释放量大小为Pb>Mn>Zn>Cu，添加生物炭后明显降低了重金属的累积释放量。对土壤中金属释放过程进行数学方程拟合后发现，应用Elovich方程能较好地描述重金属释放过程，说明这4种重金属元素在土壤中的淋溶和释放过程的机制不是单一反应过程，而是属于活化能变化较大的复杂反应过程。加入生物炭后各重金属的b值均低于对照组，重金属迁移速率随着生物炭的添加而降低，说明生物炭能提高土壤对重金属离子的吸附力，降低因土壤淋溶作用而引起的重金属迁移，可以实现对重金属复合污染矿区土壤的修复。

关键词: 矿区土壤, 重金属, 生物炭, 淋溶, 迁移, 释放特征

CLC Number:

Zhe WANG,Yifei LUO,Chunli ZHENG,Xuefeng ZHANG,Weida WANG,Qinghong JIANG. Effect of biochar on migration of heavy metals in mining soil under leaching conditions[J]. Chemical Industry and Engineering Progress, 2020, 39(2): 738-746.

王哲,骆逸飞,郑春丽,张雪峰,王维大,姜庆宏. 淋溶条件下生物炭对矿区土壤中重金属迁移的影响[J]. 化工进展, 2020, 39(2): 738-746.

Figures/Tables 6

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形态	Cu元素各形态的质量分数/%				Zn元素各形态的质量分数/%				Pb元素各形态的质量分数/%				Mn元素各形态的质量分数/%
形态	r_c=0	r_c=1	r_c=3	r_c=5	r_c=0	r_c=1	r_c=3	r_c=5	r_c=0	r_c=1	r_c=3	r_c=5	r_c=0	r_c=1	r_c=3	r_c=5
酸可提取态	17.43	14.23	8.77	5.78	24.43	21.23	18.02	15.10	28.57	25.78	21.99	16.81	9.52	7.23	5.02	2.81
可还原态	13.08	13.95	14.83	16.71	27.00	20.13	25.45	31.68	37.14	28.78	24.32	18.08	54.20	52.13	48.45	45.68
可氧化态	49.32	47.91	45.62	43.69	10.61	17.17	10.38	6.14	26.43	27.54	28.16	28.74	1.27	2.52	3.80	7.67
残渣态	20.17	23.91	30.78	33.82	37.96	41.47	46.15	47.08	7.86	17.90	25.53	36.37	35.01	38.12	42.73	43.84

形态	Cu元素各形态的质量分数/%				Zn元素各形态的质量分数/%				Pb元素各形态的质量分数/%				Mn元素各形态的质量分数/%
形态	r_c=0	r_c=1	r_c=3	r_c=5	r_c=0	r_c=1	r_c=3	r_c=5	r_c=0	r_c=1	r_c=3	r_c=5	r_c=0	r_c=1	r_c=3	r_c=5
酸可提取态	17.43	14.23	8.77	5.78	24.43	21.23	18.02	15.10	28.57	25.78	21.99	16.81	9.52	7.23	5.02	2.81
可还原态	13.08	13.95	14.83	16.71	27.00	20.13	25.45	31.68	37.14	28.78	24.32	18.08	54.20	52.13	48.45	45.68
可氧化态	49.32	47.91	45.62	43.69	10.61	17.17	10.38	6.14	26.43	27.54	28.16	28.74	1.27	2.52	3.80	7.67
残渣态	20.17	23.91	30.78	33.82	37.96	41.47	46.15	47.08	7.86	17.90	25.53	36.37	35.01	38.12	42.73	43.84

土壤层/cm	Pb/%		Cu/%		Zn/%		Mn/%
土壤层/cm	CK	5%生物炭	CK	5%生物炭	CK	5%生物炭	CK	5%生物炭
0～5	42.40	48.49	46.66	48.79	44.46	46.38	48.81	49.65
5～10	42.14	46.23	45.97	47.59	42.78	47.13	46.97	47.43
10～15	8.89	3.37	5.31	2.64	7.53	4.38	2.37	1.89
15～20	6.55	1.89	2.05	0.97	5.21	2.08	1.83	1.01

土壤层/cm	Pb/%		Cu/%		Zn/%		Mn/%
土壤层/cm	CK	5%生物炭	CK	5%生物炭	CK	5%生物炭	CK	5%生物炭
0～5	42.40	48.49	46.66	48.79	44.46	46.38	48.81	49.65
5～10	42.14	46.23	45.97	47.59	42.78	47.13	46.97	47.43
10～15	8.89	3.37	5.31	2.64	7.53	4.38	2.37	1.89
15～20	6.55	1.89	2.05	0.97	5.21	2.08	1.83	1.01

重金属	土壤	一级动力学方程			Elovich方程			双常数速率方程			抛物线扩散方程
重金属	土壤	a	b	R²	a	b	R²	a	b	R²	a	b	R²
Pb	CK	1.9949	0.0007	0.5770	-13.0950	4.5055	0.9584	-0.1395	0.4384	0.8875	3.8416	0.4209	0.8727
	5%生物炭	0.8687	0.0003	0.4106	-0.0322	0.5144	0.9619	-0.1521	0.2047	0.7719	2.0064	0.0439	0.6164
Cu	CK	0.9154	0.0008	0.6603	-6.8851	2.0499	0.9825	-1.5290	0.5063	0.9552	0.7180	0.1956	0.9332
	5%生物炭	-0.2972	0.0005	0.5099	-0.5501	0.2840	0.9510	-1.8620	0.3201	0.8098	0.5259	0.0262	0.8440
Zn	CK	1.2705	0.0007	0.7125	-6.6953	2.2190	0.9775	-0.6922	0.4095	0.9714	1.5260	0.2121	0.9221
	5%生物炭	0.0914	0.0004	0.3948	-0.3527	0.3153	0.9545	-1.2589	0.2705	0.7493	0.8895	0.0272	0.6626
Mn	CK	1.4150	0.0008	0.6734	-10.3660	3.1600	0.9899	-0.9105	0.4827	0.9544	1.3091	0.3033	0.9516
	5%生物炭	0.5674	0.0003	0.6457	-0.3448	0.4511	0.9835	-0.4807	0.2170	0.9344	1.3592	0.0418	0.8814