Bentonite is a clay with montmorillonite as its main component. Montmorillonite by complexation of the surface hydroxyl groups and a negatively charged cation-exchange surface of the crystallites of heavy metals adsorption. Because of its good adsorption performance and Smith, it was found that montmorillonite can adsorb organic cations such as hydrazine from aqueous solution. Nassen et al. purified natural bentonite to remove P b ²⁺ in solution. Under the optimal conditions, the removal rate can reach 98%. E.Alvarez - Ayuso and A. Ganchez-Sanchez used calcium-based montmorillonite and sodium-based montmorillonite to adsorb heavy metal ions in electroplating industrial wastewater, and found that treatment of electroplating wastewater with sodium-based montmorillonite is an effective method. In recent years, a series of studies have been carried out using bentonite to treat heavy metal ions in wastewater.

The use of bentonite to treat sewage is not only simple, effective, and low in cost, but also has a low release rate of heavy metals during desorption, and is less prone to secondary pollution. It is a rare sewage treatment agent. China's bentonite is rich in resources, laying a foundation for its application in wastewater treatment. There have been many reports on the treatment of nickel- containing wastewater by various modified bentonites at home and abroad. However, there are relatively few studies on the adsorption of Ni ²⁺ by calcium-based bentonite and sodium-salt in China. In this paper, the removal effects of the bentonite bentonite and its sodium soil on the Ni2+-containing simulated wastewater were compared, and the suitable conditions for Ni ²⁺ in the two soil treatment wastewaters were found.

First, the experimental part

(1) Experimental materials

The bentonite used in the experiment was taken from a certain place and was a calcium-based bentonite. The tested montmorillonite content is 61.7%. Other impurity minerals include: kaolinite (0%-6%), illite (2%-8%), feldspar (2%~l1%), quartz (2%). ~9%), gypsum (0-20%) and cristobalite (1% to 8%). The cation exchange capacity was 60.6 8 mmol/100 g, the BET surface area was 20 m 2 /g, the colloidal price was 62 ml/15 g, and the expansion ratio was 9. Its chemical composition is shown in Table 1. Preparation of sodium soil: Mix a certain amount of original soil with 3% sodium carbonate, add water to make pulp, the liquid-solid ratio is 5:1, stir for 30 minutes, and let stand to remove the bottom sand. High speed centrifugation, solid-liquid separation. Bake, smash, over 200 mesh.

(2) Experimental instruments

721 Spectrophotometer (Shanghai No.3 Instrument Factory), pHS-3C Acidity Meter (Shanghai Yulong Instrument Co., Ltd.), A Wl 20

Table 1 Chemical composition of calcium bentonite

One ten thousandth electronic balance (Shimadzu Corporation), HJ-5 constant temperature electromagnetic stirrer (Jiangsu Jintan Instrument Factory), GL-2 0 G-11 high speed refrigerated centrifuge (Shanghai Anting Scientific Instrument Factory).

(3) Experimental methods

Take 50ml of a certain concentration of Ni ²⁺ solution prepared in a beaker, add a certain amount of 200% original soil and sodium carbonate, adjust the pH value with NaOH or HCl, and adsorb it for a certain time on a constant temperature magnetic stirrer. ,filter. The mass concentration of heavy metal ions was determined by the diacetyl ketone spectrophotometry (GB11910.89).

Second, the results and discussion

(1) Influence of the amount of bentonite

Take 50 ml of water sample with initial concentration of Ni ²⁺ of 25 mg/L, add different amounts of 200-mesh original soil and sodium carbonate, stir at room temperature and natural pH for 15 min, and test the effect of bentonite dosage on Ni2+ removal rate. The result is shown in Figure 1b. Take 50ml of water with an initial concentration of 25mg/L of Ni2+, add different amounts of 200% original soil and sodium carbonate, stir at room temperature and natural pH for 15min, and test the effect of bentonite dosage on Ni2+ removal rate. See Figure 1(a).

It can be seen from Fig. 1(a) that as the amount of bentonite increases, the removal rate of Ni ²⁺ begins to increase rapidly and then slowly. When the amount of sodium soil and original soil is 10g/L and 40g/L, respectively, the removal rate of Ni ²⁺ can reach more than 96%, and the residual concentration of Ni2+ after adsorption is 0.963mg/L and 0.996mg respectively. /L, has reached the national "Integrated Wastewater Discharge Standard" (<l mg/L) issued in 1996, but the increase in soil volume has no obvious effect on the removal rate of Ni ²⁺ . In order to compare the adsorption effect of the original soil and the sodium soil on Ni ²⁺ , the amount of the two soils selected in this experiment is 10 L.

(two) the impact of mixing time

The initial concentration of Ni ²⁺ was 25mg/L water sample 50m l, respectively added to the original soil and sodium carbonate l 0 L, room temperature and natural pH conditions, the effect of stirring time on the removal rate of Ni ^{2+ was} tested. The result is shown in Figure l(b).

It can be seen from Fig. 1(b) that the adsorption rate of Ni ²⁺ ions in bentonite is very fast in the first 15 min of adsorption, and the adsorption equilibrium can be achieved after adsorption for 15 min, and then the adsorption speed is slowed down. As the adsorption time is prolonged, the amount of adsorption also slowly increases. The stirring time was chosen to be 15 min in this experiment.

(3) Influence of initial ion concentration

50 ml of water samples with different initial concentrations of Ni ²⁺ were added, and sodium carbonate and original soil were added at 10 mg/L respectively. The mixture was stirred at room temperature and natural pH for 15 min. The effect of initial ion concentration on Ni2+ removal rate was tested. The results are shown in Fig. 1. (c1).

It can be seen from Fig. 1 (C 2 ) that the removal effect of sodium soil is significantly better than that of the original soil. The amount of Ni2+ adsorbed by the unit mass adsorbent increases with the increase of the initial Ni ²⁺ ion concentration. When the concentration is greater than 25 mg/L, the increasing trend becomes larger. It can be seen from Fig. 1 (c1) that the removal rate decreases with the increase of the initial ion concentration, because the initial Ni ²⁺ ion concentration increases continuously when other conditions are constant, and the competition of Ni2+ for the adsorption site becomes equivalent. Intense, resulting in a rapid decline in the adsorption rate. When the initial ion concentration is greater than 25mg/L, the residual concentration of Ni ²⁺ after adsorption of sodium soil and original soil is higher than the national comprehensive discharge standard for wastewater. Therefore, the initial ion concentration of Ni ²⁺ was chosen to be 25 mg/L.

(4) The effect of pH

Take 50 ml of water with an initial concentration of 25 mg/L of Ni ²⁺ , add 10 g/L of sodium soil and original soil, stir at room temperature for 15 min, adjust the p value of the solution with NaOH or HC1, and test different pH values ​​for Ni. The effect of ²⁺ removal rate is shown in Figure 1(d).

Influence of multiple factors on Ni ^{2 +} removal

It can be seen from Figure I(d) that the pH of the initial solution is an important parameter in the adsorption process, and the removal rate of Ni ²⁺ increases as the pH value of the solution increases. When the pH value is less than 4, Ni ²⁺ in the solution is in a cationic state. Due to the high H ⁺ concentration, H ⁺ has competitive adsorption on Ni ²⁺ and occupies the adsorption site of the adsorbent, so Ni ^{2 at} low pH. The removal effect of ⁺ is poor. As the pH value of the solution increases and the nickel ions still exist in the ionic state, the influence of H+ competition is weakened. At this time, the exchange-adsorption properties of clay to nickel ions are mainly manifested. When the pH is further increased to alkaline conditions, the nickel ions in the solution form insoluble hydroxides, adhere to the clay surface, and settle with the clay, so the removal rate increases, which is related to UMSaha (2003). The results are consistent. Therefore, adsorption experiments are preferred at natural pH.

(5) The influence of temperature

Take 50 ml of water sample with an initial concentration of Ni ²⁺ of 25 mg/L, add human sodium soil and original soil l 0g/L, and stir for 15 min under natural pH conditions. The effect of temperature on Ni ²⁺ removal rate is tested. The result is shown in Figure 1(e).

It can be seen from Fig. 1 (e) that the reaction temperature has a slight influence on the experiment, and the curve shows a horizontal wave shape, which indicates that the temperature has little effect on the adsorption. Therefore, adsorption experiments can be carried out over a wide temperature range, and adsorption is generally carried out at room temperature for the sake of simplicity and economy.

Third, the best process for the treatment of nickel-containing wastewater

From the above results, it is known that the factors that have a large influence on the removal rate of nickel ions are pH value, amount of bentonite, and initial ion concentration. The optimal process of original soil and sodium soil was determined by orthogonal experiment. The three factors were selected for the orthogonal experiment of three factors and three levels. The other influencing factors were considered as fixed factors and stirred for 10 min at room temperature. The levels of orthogonal experimental factors are listed in Table 2. The orthogonal experimental arrangement was carried out with reference to the orthogonal table L9 (3 4 ), and the results are shown in Table 3.

Comparing the average values ​​of the three levels of each factor in Table 3 and their range R comparison analysis, the order of size is: A>C>B, that is, the order of influence of three factors on the wastewater removal rate is: the pH value of the wastewater >Initial ion concentration>Bentonite dosage.

The results show that the pH value of the wastewater and the initial ion concentration are the two main factors affecting the adsorption effect. The effect of pH is that the removal rate under weakly acidic and neutral conditions is significantly better than that under acidic conditions. The removal rate under alkaline conditions is mainly due to the formation of nickel hydroxide insoluble matter. The effect of bentonite dosage was increased with the increase of dosage. When the dosage of sodium soil reached 15 g/L, the removal rate was over 97%, and the concentration of Ni2+ in the solution after adsorption was 0.84 mg/L, lower than Nationally prescribed emission standards. It can be seen from Table 3 that the optimum process for the adsorption of sodium soil is A2B2C2, that is, the pH value is 6-7, the amount of bentonite is 10g/L, and the initial ion concentration is 25mg/L. Similarly, the best process for the adsorption of original soil. It is A 2 B 2 C2, that is, the pH value is 6-7, the amount of bentonite is 30 L, and the initial ion concentration is 20 mg/L. The removal effect of sodium soil is better than that of the original soil.

Table 2 Factors and levels

According to the orthogonal experiment, the best process of sodium soil is A2B2C2, that is, the pH value is 6-7, the amount of bentonite is l 0 L, and the initial ion concentration is 25 mg/L. The verification experiment was carried out under the selected process conditions, and the removal rate was 96.7% under the experimental conditions. The concentration of nickel in the water sample after treatment was 0.825 mg/L, which was lower than the national emission standard of 1 mg/L.

Table 3 Orthogonal experiment and results of nickel-containing wastewater

Fourth, the conclusion

(1) In the aqueous solution, the removal effect of sodium hydride on Ni ²⁺ is better than that of the original soil.

(B) Ni ²⁺ Handan bentonite has a high removal rate, the initial concentration of Ni ²⁺ were 25mg / L, 20mg / L, at room temperature, and natural pH value, the stirring time is 15min, the original soil and soil Na Under the conditions of 10L and 30L, the removal rate of Ni ²⁺ was 96% and 95% respectively, and the residual concentration of Ni ²⁺ in the solution after adsorption was 0.825mg/L and 0.96L, respectively. The maximum allowable emission standard (1mg/L).

(3) The removal rate of Ni ²⁺ by bentonite increases with the increase of p value of solution, the amount of bentonite increases, and the stirring time increases; it decreases with the increase of initial ion concentration.

7 Ton Diesel Forklift is Shantui brand. The forklift truck is of Japan quality but china price with 1 year warranty. Forklift export will have free tool box. Spare parts all you need can be provided. The forklift truck is Equipped with Chinese powerful and reliable engines (brand Chaochai) with excellent environmental performance; Original imported Isuzu, Mitsubishi engines are optional.