110

Currently, a copper-containing wastewater treatment method of chemical precipitation, electrolysis, ion exchange method or the like, wherein the ion exchange with good stability, easy to separate, reusable resin, etc., in catalysis, adsorption, metal recycling Aspects have been widely used. The adsorption of metallic copper ions from wastewater was studied using a cation exchange resin 110 ^* resin with a functional group of -COOH. The adsorption behavior of copper(II) on 110 ^* resin was investigated.

First, the test part

(1) Main reagents and instruments

110 ^* Resin (product of Nankai University Chemical Plant, particle size 354 μm; NaAc-HAc buffer solution with pH of 3.58-6. 23; copper ion standard solution, prepared by analytically pure CuSO ₄ · 5H ₂ O; other reagents were of analytical grade.

UV-1610PC ultraviolet spectrometer; ZHWY-100C constant temperature culture oscillator; pHS-3C pH meter; Burker-TEN-SOR27 infrared spectrometer.

(2) Adsorption and analysis methods

1. Adsorption equilibrium test

Weigh a certain amount of 110 ^* resin, add a certain volume of buffer solution, soak for 24 h, add a certain amount of Cu ²⁺ standard solution, shake to equilibrium in a constant temperature culture shaker, analyze the equilibrium concentration of Cu ^{2+ in the} aqueous phase, Calculate the distribution ratio (D):

Where: Q-resin adsorption amount of Cu ²⁺ , mg/g; ρ ₀ and ρ _e - are the initial mass concentration and equilibrium mass concentration of Cu ²⁺ in the aqueous phase, respectively, mg/mL; m-resin quality , g; V-liquid phase volume, mL.

2, analysis method

0.25 mL of the solution to be tested was placed in a 25 mL volumetric flask, and 1 mL of xylenol orange (0.5%) and 10 mL of HAc-NaAc buffer solution (pH=5.53) were added and diluted to the mark with double distilled water. At a wavelength of 576.3 nm, the absorbance was measured using a 1 cm cuvette with a reagent blank as a reference, and the adsorption rate and the partition ratio were calculated.

3. Desorption test

A certain amount of the loaded resin was taken, washed three times with a buffer solution, a desorbent was added, and the concentration of Cu ^{2+ in the} aqueous phase was measured after shaking balance, and the desorption rate was calculated.

Second, the results and discussion

(1) Effect of medium pH on distribution ratio

Accurately weigh 8 parts of 15.0 mg of resin, respectively, under the conditions of T=298K and ρ ₀ =167μg/mL, intermittently shake to equilibrium, and determine the effect of medium pH on the adsorption of Cu ²⁺ on the resin in HAc-NaAc buffer system. Figure 1 shows. It can be seen that when pH=4.19, the Cu ²⁺ adsorption rate is the largest, lgD=3.71. After pH>4.19, the system undergoes hydrolysis. The following tests were carried out in a HAc-NaAc system at pH = 4.19.

Figure 1 Effect of pH on distribution ratio

(2) Determination of adsorption rate and apparent activation energy

15.0 mg of the resin was accurately weighed, and an adsorption equilibrium test was carried out under conditions of T = 298 K, pH = 4.19, and ρ ₀ = 200 μg / mL. The residual mass concentration of Cu ²⁺ in the solution was measured at regular intervals until equilibrium. The measured series of data is converted into the corresponding adsorption amount after volume correction, and the graph is obtained by plotting Q~t.

Figure 2 adsorption rate curve

Adsorption of Cu ²⁺ on 110 ^* resin, in the initial stage, conforms to the rate equation

-ln(1-F)=kt+c

Where: F = Q _t /Q _∞ , Q _t and Q _∞ are the reaction time t and the adsorption amount per gram of resin at equilibrium, respectively. Figure 3 is plotted with -ln(1-F) versus t. 110 ^* Cu ²⁺ Adsorption apparent rate constant ^{_{k 298 = 1.55 × 10 -4 S}} -1 determined from the slope of the line in FIG. 3, the correlation coefficient r = 0.9722, shows that the adsorption process is diffusion film master step. Change the temperature, other conditions and methods are unchanged, and obtain the linear relationship curve of -ln(1-F)~t at 308K and 318K respectively (see Figure 3), and obtain k ₃₀₈ =2.83×10 ^-4 S ^-1 ,k ₃₁₈ = 4.20 × 10 ^-4 S ^-1 . According to the Arrhenius formula

Lgk=-E _a /2.303RT+lgA,

Figure 4 is plotted as lgk ~ 1 / T, and the apparent activation energy E _a = 37.2 kJ / mol according to Figure 4.

Figure 3 adsorption rate constant curve

Figure 4 Activation energy measurement curve

(3) Isothermal adsorption curve

Accurately weigh 15.0, 20.0, 25.0, 30.0, 35.0mg resin 5 parts, under the conditions of T=298K, pH=4.19, ρ ₀ =267μg/mL, test according to 1.2.1 method, determine the solution concentration ρ _{e at} equilibrium , converted into the corresponding adsorption amount Q, according to Freundlich isotherm Q = aρ _e ^{1 /6} , lgQ is plotted against lgρ _e . The correlation coefficient of the straight line in the figure is r = 0.9882, from which the constant b = 5.59 can be obtained. The value of b is between 2 and 10, indicating that the reaction of adsorbing Cu ²⁺ by 110 ^* resin is easy to proceed.

Figure 5 Freundlich isotherm curve

(4) Influence of temperature on adsorption and determination of thermodynamic parameters

Accurately weigh 3 parts of 15.0 mg of resin, and determine the distribution ratio of Cu ²⁺ adsorbed by the resin at 298, 308, and 318 K under the conditions of ρ ₀ = 200 μg/mL and pH = 4.19. Plot lgD versus T ^-1 × 10 ³ to obtain Figure 6. The linear correlation coefficient r=0.9994 in the figure indicates that the elevated temperature is favorable for adsorption, the adsorption process is endothermic, and the adsorption reaction is chemical adsorption. The slope of the line is k==0.773×10 ³ and the intercept is 6.26. From lgD = - ΔH / 2.303RT + ΔS / R, ΔH = 14.8 kJ / mol, ΔS = 52.0 J / (mol · K) was obtained. When T = 298 K, ΔG = ΔH - T ΔS = -0.7 kJ / mol, indicating that the resin adsorbed Cu ²⁺ can spontaneously proceed under the conditions.

Figure 6 Effect of temperature on distribution ratio

(5) Infrared spectroscopy

110 ^* Resin adsorption of Cu ²⁺ for chemisorption, indicating that the resin functional group binds to Cu ²⁺ to form a chemical bond. In order to further confirm the above speculation, the infrared spectrum before and after the adsorption of Cu ²⁺ by the resin was measured. The results show that after the adsorption of Cu ²⁺ , the absorption peak of C-OH bond on the resin at 3435.5 cm ^-1 shifts to 3467.7 cm ^-1 , indicating that the exchange of H in C-OH leads to the enhancement of C-O bond. . The characteristic absorption peak of C=O bond at 1672 cm ^-1 is obviously weakened, indicating that O in the C=O bond is coordinated with Cu ²⁺ and thus the strength of C=O bond is weakened, so that red shift occurs.

(6) Desorption and recovery of copper

30 mL (0.1-2.0 mol/L) HCl solution was added to each of 110 parts of 110 ^* resin adsorbed with an equivalent amount of Cu ²⁺ , and the mass concentration of Cu ^{2+ in the} aqueous phase was measured by shaking balance. The results are shown in Table 1. Desorption was performed with 1.0 mol/L HCl solution. The desorption rate was 50.6% at 4 min, and the desorption rate was 95.9% at 6 min. Desorption was complete at 10 min. Desorption is easy to perform, indicating that HCl is a practical desorbent.

Table 1 Desorption test results of different concentrations of hydrochloric acid solution

After Cu ²⁺ was adsorbed, it was eluted with 1.0 mol/L HCl solution, and the resin was washed twice with double distilled water, and then subjected to adsorption-desorption test three times. As a result, the adsorption capacity hardly changed, and it was confirmed that the 110 ^* resin was very Excellent regenerative capacity and recyclable.

Third, the conclusion

(a) 110 ^* Resin can be used to adsorb Cu ²⁺ from solution. At pH=4.19, the static saturated adsorption capacity was 240 mg/g; the desorption was desorbed with a concentration of 1.0-2.0 mol/L HCl solution, and the desorption rate was nearly 100.0%.

(2) The process of resin adsorption of Cu ²⁺ conforms to the Freundlich empirical formula, the adsorption reaction is easy to carry out, and the adsorption process is controlled by chemical reaction.

(3) The thermodynamic parameters of resin adsorption of Cu ²⁺ are: â–³H=14.8kJ/mol, â–³S=52.0J/(mol·K), â–³G=-0.7kJ/mol, apparent activation energy E _a =37.2 kJ/mol, apparent rate constant k ₂₉₈ = 1.55 × 10 ^-4 S ^-1 .

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