Experimental study on removal of high concentration sulfate ion in gold ore beneficiation wastewater

With the rapid development of national economy, gold demand increases rapidly, increasing production in 2006, China's gold output reached 110t. However, each treatment of 1t gold ore requires 3t of water and nearly 20t of drainage. It is estimated that the annual discharge of gold ore dressing wastewater is nearly 1.2 billion tons [1] . At present, most gold mines in China have high sulfur content and complete high-concentration sulfate wastewater after catalytic oxidation. However, due to cost or geography, gold ore beneficiation uses water from beneficiation wastewater, but the ore dressing wastewater is high in SO 4 2 - content. As a result, the density is large, which seriously affects recycling and even efflux. Therefore, a large amount of fresh water is needed every day, which greatly increases operating costs, and the discharged wastewater causes great pollution to the surrounding environment. There have been many studies on the removal methods of SO 4 2 - at home and abroad, mainly including neutralization method, redox method, ion exchange method, biodegradation method, etc. [2 ~ 6] , but mainly for low concentration beneficiation wastewater such as copper and zinc . The removal of SO 4 2 - in the middle, and the disadvantages of high cost, complicated process and inconvenient management, but little research on the removal of high concentration SO 4 2 - in gold ore beneficiation wastewater, based on this, find a low cost and simple process. The high concentration SO 4 2 - removal process with good treatment effect, convenient operation and strong impact resistance is the research purpose of this experiment.

First, materials and methods

(1) Sewage water quality

The test water taken from a gold mine in Guizhou is the effluent of the tailings plate and frame filter press in the mining area, and the appearance is turbid. According to the barium sulfate turbidimetry-ultraviolet spectrophotometry, the SO 4 2 - concentration in the wastewater is accurately determined to be 3684.6 mg/L. . Refer to the "Design Code for Industrial Circulating Cooling Water Treatment" [7] and "Emission Standards for Pollutants in Heavy Nonferrous Metals Industry" [8] , and combine the actual conditions of ore dressing water in the plant to propose wastewater reuse or discharge standards. The water quality characteristics of the mining area and the reuse or discharge standards are shown in Table 1.

Table 1 Wastewater quality characteristics and reuse/emission design standards

(2) Test equipment and pharmacy

Test equipment: UV-2000 ultraviolet spectrophotometer, FA2004 electronic molecular balance, MY3000-6B coagulation test six-coupler, GSP-80-04 magnetic stirrer, PHS-3B precision acidity meter, beaker, etc. .

Main agent: anhydrous sodium sulfate, sodium chloride, hydrochloric acid, glycerol, ethanol, barium chloride, deionized water, lime (CaO), polyaluminum chloride (PAC), polyacrylamide (the PAM), active oxygen Aluminum and so on.

(3) Test methods

According to the test water quality and design standards, the combination process of quicklime + PAC + PAM + activated alumina is used. The test procedure is:

1. Add 500 ml of raw water to each of several beakers, add different doses of quicklime to carry out the reaction, and determine the optimum amount of lime dosage according to the concentration of SO 4 2 - in the effluent. According to the optimal dosage, the value of each influencing factor is determined by single factor test.

2. Add 500 ml of raw water to each of the several beakers, add the optimum amount of lime determined in step 1, and then add different doses of PAC to determine the optimum amount of PAC according to the concentration of SO 4 2 - in the effluent. According to the optimal dosage, the value of each influencing factor is determined by single factor test.

3. Add 500ml of raw water to each beaker, add the optimal dosage of the drug determined in steps 1, 2, and then add different doses of PAM to determine the best PAM dosage according to the concentration of SO 4 2 - in the effluent. the amount. According to the optimal dosage, the value of each influencing factor is determined by single factor test.

Second, the results and discussion

(1) Removal effect of quicklime dosage on SO 4 2 -

The variation curves of different quicklime dosages for SO 4 2 - removal are shown in Fig. 1. It can be seen that the removal effect of quicklime on SO 4 2 - is not significant, the maximum removal rate is only about 40%, and the optimum dosage is 7g/L, because during the reaction, the calcium sulfate formed is slightly soluble. adsorbed on the surface quicklime to form calcium sulfate dense layer of film, the influence of the Ca 2 + 4 2 and SO - reaction was continued, and continues as lime dosing, due to the protective effect of calcium sulphate film, but removal decline.

Fig.1 Change curve of quicklime to SO 4 2 - removal

(2) Removal effect of quicklime + PAG on SO 4 2 -

Polyaluminum chloride PAC can neutralize the charge and compress the electric double layer, causing the colloidal particles to coagulate and bridge each other. Under certain hydraulic conditions, it can form larger flocs with SO 4 2 - , and the precipitation can achieve the removal effect. after the optimum dosage lime (7g / L) of the reaction, the PAC collaborative study of SO 4 2 - removal of [9-11]. The removal curve of the quicklime + PAC combination agent for SO 4 2 - is shown in Fig. 2. It can be seen that the optimal dosage of PAC is 20 mg/L. When the dosage of PAC is less than 20 mg/L, part of the colloidal particles cannot be The removal by the action of the coagulation mechanism such as the compressed electric double layer affects the removal effect and the removal rate is low. When the coagulation dose is greater than 20 mg/L, the coagulated hydrolyzate cannot be colloidal as the core and reaches the volume of the sweeping net. The effect is suspended in the liquid, and the formed floc is adsorbed around the particles, and the removal effect is not obtained, and the removal rate is decreased.

Fig. 2 Change curve of SO 4 2 - removal by quicklime + PAC combination

(III) Removal effect of quicklime + PAC + PAM on SO 4 2 -

In order to increase the flocculation effect and increase the formation and compactness of the scented flower, the coagulant polyacrylamide PAM is added after the PAC is added. PAM is an organic polymer flocculant which is polymerized from acrylamide. The main chain of the molecule contains an enamide amide PAM. PAM has a large number of pendant amide groups. The amide group has strong chemical activity and can react with various compounds to produce many polyacrylamide derivatives. The molecular chain group can be compared. The distant particles form a polymer bridge, which increases the number of collisions, so that some of the neutralized colloidal particles are quickly adsorbed and bridged, which can greatly enhance the formation and precipitation of the flocculated flocs [12 ~ 14] .

After the reaction of the best quicklime dosage (7g/L) and the best PAC dosage (20mg/L), PAM was added to carry out the experimental study. The removal curve of the seedlings of the lime 10 PAC and the PA 4 2 - was obtained. Figure 3, it can be seen that the removal of SO 4 2 - after the addition of coagulant is obvious, the optimal PAM dosage is 10mg / L, less than 10mg / L, the collision chance of particles is less, the formation rate of floc and The sedimentation rate is slow and the removal rate is low. However, when the PAM dosage is more than 10 mg/L, the adsorption point of the flocculant particles is rapidly occupied, which reduces the possibility of bridging, and the flocculation effect decreases.

Figure 3: Slim lime + PAG + PAM versus SO 4 2 - removal curve

(4) Removal effect of activated alumina on SO 4 2 -

Activated alumina is a porous, highly dispersible, bulk material with a large surface area and permeability. When SO 4 2 - collides with a solid surface, it is attracted by an unbalanced force and stays on the solid surface. Remove the purpose. After the optimal coagulant treatment, the activated alumina was further added to the supernatant for adsorption, and the SO 4 2 - removal curve is shown in Fig. 4. According to the adsorption mechanism, when the dosage is less than 22g/L, the adsorption is mainly used for the interaction of the layer, and the adsorption effect increases with the increase of the dosage, but when the coagulant is greater than 22g/L, the adsorbent is SO 4 2 - The adsorption reached saturation, and the adsorption effect was not obvious with the increase of dosage. For example, the increase of 20g/L to 32g/L, the treatment rate only increased from 88.2% to 88.3%, from the treatment cost and efficiency analysis, The optimum active alumina dosage was 22 g/L.

Fig. 4 Change curve of activated alumina on SO 4 2 - removal

(V) Analysis of influencing factors

1. Effect of reaction time on removal effect

The appropriate reaction time is beneficial to the coagulation agent and the pollution factor to fully react, to achieve the best removal effect, the time is too short, the reaction is not sufficient, and the time is too long, not only can not increase the removal effect, but energy consumption, different reaction time to SO The removal effect of 4 2 - is shown in Figure 5. It can be seen that the optimum reaction time of lime, PAC and PAM is l8, l4, 12min respectively.

Figure 5 Removal effect of SO 4 2 - with different reaction times

2. Effect of stirring intensity on removal effect

Choosing the right agitation intensity is beneficial to the coagulant to accelerate the flocculation process and improve the flocculation effect. The stirring speed is too slow, the distribution of the agent in water is not uniform, and it can not be in full contact with the colloid or contaminant particles, which is not conducive to the capture of colloids or particles by the agent; and the stirring speed is too fast, which will cause the large colloid or fine floc which is about to be precipitated to be stirred. Broken, turned into small flocs that can not settle and reduce the flocculation effect [15 ~ 16] . The removal effect of SO 4 2 - with different stirring strength is shown in Fig. 6. It can be seen that the optimum stirring strengths of lime, PAc, PAM and activated alumina are 200, 150, 100, 150 r/min, respectively.

Figure 6 Removal effect of SO 4 2 - with different stirring speed

3. Effect of sedimentation (adsorption) time on removal effect

Selecting a reasonable settling time is conducive to the complete flocculation precipitation, and a reasonable adsorption time is beneficial to the adsorption and adsorption factors of the adsorbent and the pollution factor to achieve the best balance of adsorption. When the time is too short, the precipitate is not sufficiently precipitated (adsorbed), affecting the removal rate, and the excessive removal rate is almost unchanged. The removal effect of different precipitation (adsorption) time on SO 4 2 - is shown in Fig. 7. It can be seen that the optimum precipitation time of lime, PAC and PAM is 30, 25 and 20 min, respectively, and the optimum adsorption time of activated alumina is 50 min.

Figure 7 Removal effect of different precipitation (adsorption) time on SO 4 2 -

Third, the conclusion

1. The lime ore + PAC + PAM + activated alumina process was used to treat the gold ore beneficiation wastewater towel sulfate. The final concentration of SO 4 2 - in the water was 435.6 mg / L, the removal rate reached 88.2%, and the water sample density was 1.048 g / ml. It can fully meet the water quality requirements of the ore dressing water in the mining area, and can also meet the requirements of the "Emission Standard for Pollutants in Heavy Nonferrous Metals Industry".

2. Through single factor test and orthogonal test, the optimal dosage of SO 4 2 - in this combined process is lime 7g/L, PAC 20mg/L, PAM10mg/L, and activated alumina 22g/L. The optimum stirring speeds of lime, PAC, PAM and activated alumina are 200, 150, 100, 150r/rain, respectively. The optimum reaction time of lime, PAC and PAM is 18, 14, 12rain respectively, and the precipitation time is 30, respectively. At 25 and 20 min, the optimum adsorption time of activated alumina was 50rain.

3. The combined process is simple, the treatment efficiency is high, the operation is stable and reliable, and it has certain impact resistance. It can adapt to the sharp change of SO 4 2 - in the external drainage, and can minimize the environmental impact caused by the efflux of sulfate wastewater. Pollution has certain practical value for the current problem of high recovery ratio of SO 4 2 - in most gold ore beneficiation wastewater.


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