The effect of humic acid and fulvic acid on adsorption-desorption behavior of copper and zinc in the yellow soil

The effect of humic acid and fulvic acid on adsorption-desorption behavior of copper and zinc in the yellow soil Zhantai Wang, Minxia Cao, Wenchang Cai, and Heping Zeng Citation: AIP Conference Proceedings 18, 427 (17); View online: https://doi.org/1.163/977299 View Table of Contents: http://aip.scitation.org/toc/apc/18/1 Published by the American Institute of Physics Articles you may be interested in Adsorption of humic acid from landfill leachate by nitrogen-containing activated carbon AIP Conference Proceedings 1794, 33 (17); 1.163/971925 Isolation of humic acid from peat soil and its application as an adsorbent for AuCl 4 - in solution AIP Conference Proceedings 1823, 39 (17); 1.163/978112 The novel kinetics expression of Cadmium (II) removal using green adsorbent horse dung humic acid (Hd-Ha) AIP Conference Proceedings 1823, 1 (17); 1.163/97874

The Effect of Humic Acid and Fulvic Acid on Adsorption- Desorption Behavior of Copper and Zinc in the Yellow Soil Zhantai Wang a), Minxia Cao b), Wenchang Cai c) and Heping Zeng d) School of Kunming University of Science and Technology, Kunming 655, China. a) 134513735@qq.com b) 54654585@qq.com c) c_kmstyle@163.com d) Corresponding author: dabatou@126.com Abstract. The adsorption-desorption behavior of copper(cu) and zinc(zn) and the influencing factors are very important for the evaluation of migration behavior of Cu(II) and Zn(II) in the soil environment. The study is aimed to research the effect of humic acid (HA) and fulvic acid (FA) on adsorption-desorption behavior of Cu (II) and Zn (II) in the yellow soil. The results showed that the effect of HA and FA on adsorption-desorption behavior of Cu (II) and Zn (II) varies with different concentrations of Cu (II) and Zn (II). In the presence of HA, there is less adsorption amount of Cu (II) in soil. In addition, HA is not conducive to soil Zn-adsorbing at initial low concentration of Zn (II). However, HA is benefit to increase the adsorption amount of Zn (II) in the soil at high concentration. FA has similar effect on adsorption behavior of the Cu (II) and Zn (II). FA is not conducive to the soil adsorption of Cu (II) and Zn (II) at low concentrations. However, FA is benefit to the soil adsorption of Cu (II) and Zn (II) at high concentrations. Besides, Zn (II) adsorbed is harder to be desorbed by the neutral salt solution. Therefore, comparing with Cu (II) adsorbed, the adsorption amount of Zn (II) moves harder in the acidic yellow soil. Key words: Adsorption-desorption; acidic yellow soil; heavy metal; humic acid; fulvic acid. INTRODUCTION Cu and Zn are not only the necessary nutrients of plants, but also two kinds of concerned metal pollutants. There are so many researchers report the adsorption behavior of Cu (II) and Zn (II) and their influencing factors in the soil [1]. As wastewater irrigation and sludge utilization, a variety of molecular weight dissolved organic carbon (DOC) is introduced in the soil. As a result, they have strong complexation with heavy metal irons and form stable organicmetal complexes, which may increase or decrease the solubility of heavy metal ions and change the behavior of their migration which is cured or freed in the soil environment. Therefore, the adsorption-desorption behavior of heavy metal ions in the soil is one of the important factors that evaluated the behavior of their migration in environmental. Humus is a kind of macromolecule organic matter that exists widely in soil medium. Humic acid (HA) and fulvic acid (FA) can be isolated from humus according to the acid or alkali solubility [2, 3]. HA and FA are two kinds of common DOC in the soil. HA contains a variety of functional treatments which can interact with the heavy metals in soil [4, 5], but different ph of soil medium has a significant impact on the behavior of environment [6]. FA also has strong complexation with heavy metals and significantly affect the adsorption-desorption behavior of heavy metals in soil because of solubility of FA-metal complex. Therefore, in order to study roundly adsorption-desorption behavior of Cu (II) and Zn (II) in the presence of HA and FA in yellow soil, we set Cu (II) and Zn (II) as the research object and set HA and FA as the representatives of DOC. What s more, adsorption-desorption mechanism of Cu (II) and Zn (II) will be discussed in the presence of two kinds of DOC in soil. As a result, we could evaluate their migration behavior which is cured or freed under the action of HA and FA in the soil environment. Advances in Materials, Machinery, Electronics I AIP Conf. Proc. 18, 427-1 427-9; doi: 1.163/977299 Published by AIP Publishing. 978--7354-1488-4/$3 427-1

MATERIALS AND METHODS Soil Characterization and Chemical Reagents The soil sampling area was in the dry land of Lu village which is located at Dayao Country of Chuxiong Yi Autonomous Prefecture, Yunnan Province, China. The soil was collected from soil surface layer (cm-1 cm) and then air-dried and sieved through 2mm sieve. Besides, we removed the organic matter in the soil [7], added in 3% hydrogen peroxide to the soil and stirred until no bubbles over and over again, which is aimed at decrease the effect of DOC in yellow soil. Finally, the soil was air-dried and sieved through 2mm sieve again. The main physiochemical properties of soil including total Cu content was 33.2 mg/kg, total Zn content was 8 mg/kg, total nitrogen content was 1.94 mg/g, total phosphorus content was 437.9 mg/kg, total potassium content was 22.66 mg/g, ph was 5.64. HA and FA, as the commercially available solid material, were purchased from Shanghai Dibai Chemical Reagent Company. HA consists of 9.44% carbon, 7% hydrogen, 6.18% oxygen,.31% nitrogen,.34% sulfur and FA consists of 29.88% carbon, 4.32% hydrogen, 22.98% oxygen, 3.46% nitrogen, 3.25% sulfur. Solution Preparation Copper standard solution (concentration of Cu (II): 3 mg/l) and Zn standard solution (concentration of Zn (II): 4 mg/l) was prepared respectively as the mother liquor with Cu (NO 3) 2(AR) and Zn (NO 3) 2(AR). Then, HA mother liquor (mass concentration: 342.4 mg/l) and FA mother liquor (mass concentration: 162.4 mg/l) was prepared respectively. Total organic carbon concentration both were 249.1 mg/l. The other solution needed for the experiment was diluted from the mother liquor. In the process of dissolving HA, the ph of the mother liquid should be adjusted more than 1 and stirred it constantly. FA was easy to be dissolved so the ph of FA mother liquid didn t need to be adjusted in the process of dissolving. The respective Cu (II) concentration of the mixed solutions is mg/l, 8 mg/l, 16 mg/l, 32 mg/l, 64 mg/l, 128 mg/l, 192 mg/l; the respective Zn (II) concentration of the other mixed solution is mg/l, 1 mg/l, mg/l, 4 mg/l, 8 mg/l, 1 mg/l, 24 mg/l. The concentrations of HA and FA, respectively, are mg/l, 344 mg/l and mg/l, 16.24mg/L in the mixed solution and total organic carbon concentration of the both is 249.1 mg/l. We set the solution without Cu (II) and Zn (II) as the control treatment. The supporting electrolyte of the mixed solution about experiment was 1mol/L KNO 3 solution and the ph of all mixed solution should to be adjusted about 5.5 by using the dilute KOH and dilute HNO 3. Experiment Methods Firstly, weighed g soil sample in 5 ml plastic centrifuge tube and added 25ml mixed solution that including different concentrations of Cu(II), Zn(II), HA and FA. Then, put into the oscillator, oscillated continuously 144 min under the condition of the constant temperature of 25 degrees. After oscillation, centrifuged for 1 minutes in a centrifuge at 5 (r/min) and took supernatant to determine concentration of Cu (II) or Zn (II) and ph. The subtraction method was used to calculate the adsorption amount of Cu (II) or Zn (II). Then, 25 ml 1 mol/l KNO3 solution was added into the residual soil and oscillates continuously 144 min again. After centrifugation, took supernatant to determine concentration of Cu (II) or Zn (II). Finally, calculated the adsorption amount of Cu (II) or Zn (II) after desorption by subtraction method again. Each sample did repeat three times. Measuring Methods The concentrations of Cu (II) and Zn (II) were determined by atomic absorption spectrometer (American Varian, AA24FS). Supernatant ph was determined by ph meter (PHS-3C). Tables were drawn by Microsoft Office Excel 3 and graphs were drawn by Origin 8. 427-2

Cu( ) concentration of balanced solution/(mg/l) 1 14 1 8 4 HA HA a.4 HA HA b.4 HA.4 HA 4 8 1 14 1 18 Cu( )concentration of balanced solution/(mg/l) c 2 4 6 8 1 12 14 16 18 Cu( )concentration of balanced solution/(mg/l) d, HA, FA, 1, HA1, FA1 represent the adsorption behavior before desorption;, HA, FA, 1, HA1, FA1 represent the adsorption behavior after desorption. The same as below figures FIG. 1. The effect of HA on adsorption-desorption behavior of Cu (II) RESULTS The Effect of HA on Adsorption-Desorption Behavior of Cu (II) and Zn (II) The effect of HA on adsorption-desorption behavior of Cu (II) was shown in Fig.1. Before desorption, with the increase of Cu (II) concentration, both of the Cu (II) adsorption amounts of treatment (only Cu (II)) and HA treatment (Cu (II) and HA) were significantly increased. The Cu (II) concentration of balanced solution was also increased after oscillating continuously 144 minutes. Comparing with treatment, the Cu (II) concentration of HA treatment was higher in balanced solution and the Cu (II) adsorption amount of HA treatment was less before desorption. After desorption, the Cu (II) adsorption amount of treatment was more, compared with HA treatment. In addition, at high Cu (II) concentration of balanced solution, the tendency of Cu (II) adsorption in treatment grow faster than that in the HA treatment (Fig.1c). The effect of HA on adsorption-desorption behavior of Zn (II) was shown in Fig.2. With the increase of Zn(II) initial concentration, both of Zn(II) adsorption amount of treatment (only Zn(II)) and treatment (Zn(II) and HA) became more. The Zn (II) concentration of balanced solution was also higher after oscillating continuously 144 minutes. At initial low concentration of Zn (II), the Zn (II) concentration of treatment was higher than the Zn (II) concentration of treatment in balanced solution and the Zn (II) adsorption amount of treatment was less. However, comparing with treatment, the Zn (II) adsorption amount of treatment was more at initial high concentration of Zn (II). Besides, according to adsorption isothermal curve of treatment and treatment (Fig.2c), the adsorption amount of treatment grow faster at high Zn (II) concentration of balanced solution. 427-3

Zn( ) concentration of balanced solution/(mg/l) 1 8 4 Initial Zn( ) concentration/(mg/l) a 3. 2..5 Initial Zn( ) concentration/(mg/l) b 3. 2..5 3. 2..5 4 8 1 Zn( ) concentration of balanced solution/(mg/l} c 1 2 3 4 5 6 7 8 9 1 Zn( ) concentration of balanced solution/(mg/l} d FIG. 2. The effect of HA on adsorption-desorption behavior of Zn (II). The Effect of FA on Adsorption-Desorption Behavior of Cu (II) and Zn (II) The effect of FA on adsorption-desorption behavior of Cu (II) was shown in Fig. 3. With the increase of Cu(II) initial concentration, both of the Cu(II) adsorption amount of treatment and FA treatment (Cu(II) and FA) became more, the same as the Cu(II) concentration of balanced solution after oscillating continuously 144 minutes. At low initial concentration of Cu (II), Cu (II) adsorption amount of treatment and FA treatment were no significant differences. However, when Cu (II) initial concentration is higher than 64mg/L, Cu (II) adsorption amount of FA treatment was more than treatment. As Fig.2-1c is shown, both of the adsorption amount of FA treatment and treatment had the trend of adsorbing faster at high Cu (II) concentration of balanced solution. On contrary, the adsorption amount of the two treatments adsorb slower at low Cu (II) concentration of balanced solution. The effect of FA on adsorption-desorption behavior of Zn (II) was shown in Fig. 4. As Zn (II) initial concentration increasing, the both of Zn (II) adsorption amount of treatment and treatment (Zn (II) and FA) became more. Besides, comparing with treatment, the Zn (II) adsorption amount of treatment was more, at initial high concentration of Zn (II). Meanwhile, according to adsorption isothermal curve of treatment (Fig.4c), with Zn (II) concentration of balanced solution increasing, the adsorption amount of treatment had the trend of growing faster. However, treatment was the opposite. 427-4

Cu( ) concentration of balanced solution/(mg/l) 1 14 1 8 4 FA FA a.4 FA FA b.4 FA.4 FA 4 8 1 14 1 18 Cu( )concentration of balanced solution/(mg/l) c 2 4 6 8 1 12 14 16 18 Cu( )concentration of balanced solution/(mg/l) d FIG. 3. The effect of FA on adsorption-desorption behavior of Cu (II) The Respective Effect Of HA and FA on Cu (II) and Zn (II) Balanced Solution Ph As Fig. 5 shown, at initial low concentration of Cu (II), the balanced solution ph of HA treatment and FA treatment were lower than treatment, but in relatively high concentration, ph were obviously higher. Especially, when the initial Cu (II) concentration was 64 mg/l, the balanced solution ph of HA treatment and FA treatment were the highest. However, with Zn (II) initial concentration increasing, the balanced solution ph of all treatments showed a decreasing trend (Fig. 6). Furthermore, ph of treatment and treatment were lower than that in treatment. 427-5

( ) concentration of balanced solution/(mg/l) 1 8 4 Initial concentration/(mg/l) a 3. 2..5 Initial concentration/(mg/l) b 3. 2..5 3. 2..5 4 8 1 Zn( ) concentration of balanced solution/(mg/l) c 2 4 6 8 1 Zn( ) concentration of balanced solution/(mg/l) d FIG. 4 The effect of FA on adsorption-desorption behavior of Zn (II) 5.4 HA 5.4 FA 5.2 5.2 ph of balanced solution 5. 4.8 4.6 4.4 ph of balanced solution 5. 4.8 4.6 4.4 4.2 4.2 FIG. 5 The effect of HA and FA on ph of Cu (II) balanced solution 427-6

5.4 5.4 5.2 5.2 ph of balanced solution 5. 4.8 4.6 4.4 4.2 ph of balanced solution 5. 4.8 4.6 4.4 4.2 Initial Zn( ) concentration/(mg/l) Initial Zn( ) concentration/(mg/l) FIG. 6 The effect of HA and FA on ph of Zn (II) balanced solution the rate of special adsorption(%) 9 8 7 5 4 3 1 HA FA the rate of special adsorption(%) 9 8 7 5 4 3 1 Initial Zn( ) concentration/(mg/l) FIG. 7 The effect of HA and FA on the special adsorption of Cu (II) and Zn (II). The Difference about the Special Adsorption of Cu (II) and Zn (II) According to Fig.7, increase with initial concentration of Cu (II) and Zn (II), the rate of special adsorption (ratio of adsorption amount after desorption and adsorption amount before desorption) in all treatments were significantly increased. The rate of special adsorption in, and treatment were higher than that in, HA and FA treatment. In addition, the rate of special adsorption in FA treatment was higher than that in and HA treatment at > 32 mg/l Cu (II) treatment. However, the rate of special adsorption in treatment was higher than that in and treatment at high Zn (II) initial concentration. DISCUSSION According to present study, increase with the ph of solution, weak acidic functional treatments of HA also gradually increases and electrostatic repulsion of HA molecular surface becomes stronger. As a result, aggregated structure gradually becomes mesh structure. The surface and internal area can combine with certain metal ions [1, 8]. The other study shows that HA of aggregated structure can be adsorbed by soil easily in the acidic environment [9]. According to present results, soil and adsorption environment both are acidic. As a result, HA can be easily adsorbed by soil particles. On the other hand, HA particles surface can adsorb more hydrogen irons instead of Cu (II) in acidic solution. Furthermore, with reduce of negative charges on HA surface, the combination ability between HA and metal irons decrease greatly. Thus, HA, which adsorbed a large number of hydrogen ions, is adsorbed by soil, what s more, it also occupies adsorption sites of soil. In addition, the adsorption amount of HA treatment is less than treatment (Fig. 1b). The adsorption behavior of Cu (II) and Zn (II) effected by HA is different. At low Zn (II) initial concentration, the adsorption amount of treatment is less than that in treatment. However, comparing with treatment, the adsorption amount of treatment is higher when exposed in higher Zn (II) 427-7

initial concentration. The one of possible reasons is that HA still has chelation with the part of Zn (II) although there are still a large number of hydrogen ions in solution. So the presence of high concentration hydrogen irons has less effect on the Zn (II) adsorption. As Fig.4 shows, the ratio of treatment is bigger than treatments at initial high concentration of Zn (II). The ratio of adsorption amount before desorption and adsorption amount after desorption reflects the amount of specific adsorbing sites in soil. So HA still have chelation with the part of Zn (II). According to present results, the adsorption amount of Cu (II) and Zn (II) in FA and treatment are less than that in and treatment at the low initial concentration. However, the Cu (II) and Zn (II) adsorption amount of FA and treatment are more than and treatments at initial high concentration. FA is soluble compounds, and it also interacts with heavy metal ions to form soluble FA-metal complex. Therefore, some FA interact with Zn (II) and Cu (II) to form soluble complexes at low Zn (II) and Cu (II) initial concentration. But the other FA without interacting with metal ions can also occupy adsorption sites of soil, which lead to reducing the adsorption capacity of soil for heavy metal ions. However, complexation capacity of FA and metal irons may tend to be saturated at high initial concentration of Zn (II) and Cu (II). The rest of free metal ions and FA-metal complexes are adsorbed by soil because FA increases the total adsorption sites in soil [1]. So FA can increases the adsorption amount of Cu (II) and Zn (II). The neutral salt solution desorb metal irons adsorbed by electrostatic adsorption in soil. However, specific adsorption of soil for metal irons is hard to be desorbed by the neutral salt solution [11, 12]. According to Fig. 4c, the adsorption isotherm of before and after desorption almost overlap at and treatment, which suggested that soil adsorbted-zn (II) is hard to be desorbed by the neutral salt solution. Fig.4 also proves the phenomenon. Comparing with Cu (II), there is more specific adsorbing amount of Zn (II) in soil at all treatment. Therefore, Zn has a lower mobility than Cu in acidic yellow soil. CONCLUSION (1) In acidic yellow soil, the effect of HA and FA on adsorption-desorption behavior of Cu (II) and Zn (II) varies with different concentrations of Cu (II) and Zn (II). In the presence of HA, the soil has less adsorption amount of Cu than that in treatment. In addition, HA is not conducive to soil Zn-adsorbing at low Zn initial concentration. However, at high Zn concentration, HA is benefit to the soil adsorption of Zn. Furthermore, FA has similar effect on adsorption behavior of the Cu (II) and Zn (II). FA is not conducive to the soil adsorption of Cu (II) and Zn (II) at low concentrations. However, FA is benefit to the soil adsorption of Cu (II) and Zn (II) at high concentrations. (2) The adsorbed Zn (II) by soil is hard to be desorbed by the neutral salt solution. There is more specific adsorption ratio of Zn (II) than Cu (II). Therefore, comparing with Cu (II) adsorbed, Zn (II) adsorbed move harder in the acidic yellow soil. ANOWLEDGEMENTS The project was supported by the Natural Science Foundation of China (Program: 6492-1437). Corresponding author: Heping Zeng (1974 - ), male (Tujia), Hubei, Associate Professor, mainly engaged in soil and water conservation. dabatou@126.com. First author: Zhantai Wang (1989 - ), male (Han), Hebei, postgraduate, mainly engaged in soil and water conservation. 134513735@qq.com. REFERENCES 1. Xu, Z., et al. Competitive sorption behavior of copper (II) and herbicide propisochlor on humic acids. Journal of Colloid & Interface Science. 5, 287(2): 422-427. 2. Wen QX. Research method of soil organic substance. Beijing: Agriculture Publishing House. 1984, 234-247 3. Li GL and Wei SQ. The characteristics of adsorption and desorption of humic acids on copper. Ecology and Environmnet. 3, 12(1): 4-7. 4. Hizal, J. and R. Apak. Modeling of copper (II) and lead (II) adsorption on kaolinite-based clay minerals individually and in the presence of humic acid. Journal of Colloid & Interface Science. 6, 295(1): 1 13. 5. Matis, K. A., et al. Sorption of As (V) by Goethite Particles and Study of Their Flocculation. Water, Air, & Soil Pollution. 1999, 111(1): 297-316. 427-8

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