Experimental study on treatment of lead and zinc sulfide ore beneficiation wastewater by coagulation and adsorption

With the increasing emphasis on mine environmental protection, how to effectively treat the use of mineral processing wastewater is an important issue for mines. Indicators processing plant wastewater emissions, heavy metal concentrations of metal ions in water, suspended solids and chemical oxygen demand concentrations are much higher than the national emission standards, resulting in a great impact on the surrounding environment processing plant. This paper focuses on the treatment of wastewater treatment in the concentrator, focusing on the coagulation treatment of beneficiation wastewater, and then the method of adsorption of activated carbon. The water quality indicators of the treated wastewater have reached the national mine wastewater discharge standard. This method not only solves the problem of effluent discharge of mine wastewater. It is also reasonable to reuse the purified wastewater, so that the mine has taken a solid step toward environmentally friendly enterprises.

First, test methods and materials

(1) Test materials

The ore dressing wastewater is taken from the beneficiation workshop. The water quality analysis is shown in Table 1.

Table 1

project

Pb(mg/L)

Zn(mg/L)

Cu (mg/L)

COD (mg/L)

SS (mg/L)

PH

Foaming

Mineral processing wastewater

260

13

0.15

460

380

12.2

Strong

(2) Test reagents and equipment

Test Reagents: polyferric sulfate, polyaluminum chloride, polyacrylamide, Al 2 (SO4) 3 · 18H 2 0 ( alum), powdered activated carbon, granular activated carbon.

Test equipment: COD rapid tester, 721-type spectrophotometer, heating magnetic stirrer, PH-3 precision pH meter, photoelectric analysis balance, atomic absorption spectrometer.

Monitoring Method: Metal ion concentration - atomic absorption method, chemical oxygen demand (C0D) - weight of chromium, potassium, turbidimetry - spectrophotometry, the concentration of suspended solids (the SS) - weighing method.

Second, test results and analysis

(1) Comparison test of coagulant effect

Take a set of 500mL of ore dressing wastewater, add different types and different doses of flocculant at room temperature without adjusting the pH value of the original waste water, stir rapidly for 1min (250r/min), then stir slowly for 5min (50-80r/ Min), after standing for 30 min, the supernatant was taken to determine the remaining turbidity. The treatment effect is shown in Table 2.

Table 2

Measured by each metal ion concentration mg/L

Turbidity removal rate%

5

Polyferric sulfate

Polyaluminum chloride

alum

10

55

75

76

15

62

83

84

20

64

87

85

25

71

94

90

30

73

91

93

It can be seen from Table 2 that the coagulation effect of the polymerized ferric sulfate is not ideal when the pH is not adjusted, because the optimum pH of the coagulation is not reached, and the coagulation with polyaluminium chloride or alum is used. The effect is better, the water molecules coordinated by the hydrated aluminum ions dissociate, can produce a variety of hydroxy aluminum ions, and form polynuclear hydroxy compounds, which can not only neutralize the negative charge on the surface of the colloid, but also when the degree of polymerization is high. In order to bridge the colloidal particles, the cohesion of this form is the strongest. Because the chloride ion in the polyaluminum chloride affects the determination of COD in wastewater, it is more reasonable to use alum as a coagulant from the perspective of cost. The optimum dosage is 30mg/L.

(B) the effect of polyacrylamide PAM on coagulation

Polyacrylamide PAM is an organic polymer flocculant which has a good effect on removing suspended particles and is not affected by p H and metal ions. The group in the molecular chain can be between the distant particles. The formation of a polymer bridge can greatly accelerate the formation and precipitation of the flocculated floc, and because of the large elongation of the molecular weight polymer in water, it is more advantageous for the two negatively charged colloidal particles to cross the potential energy peak and If the bridge is connected, if a certain amount of alum is added first, then PAM is added, initially the charge neutralization of alum, so that the surface charge of the high concentration raw water is neutralized to a certain extent, the colloidal repulsive energy can be weakened, and the mutual mutual The number of collisions, followed by the addition of PAM, allows the partially neutralized colloidal particles to be quickly adsorbed and bridged to form flocs. The test is carried out under the conditions of the best dosage of alum (30mg/L), and the other conditions are the same as test (1). The test results are shown in Table 3.

table 3

0.1% PAM (mg/L)

0

0.2

0.5

1

5

Pb(mg/L)

3.2

O.92

0.95

1

0.8

COD (mg/L)

393

395

398

400

421

Turbidity removal rate%

93

96

96.8

97

98.2

It can be seen from Table 3 that the addition of a small amount of PAM further improves the coagulation treatment effect of the wastewater, but since it is an organic polymer, the COD value in the water is slightly increased, and the change in the coagulation treatment effect and the increase in the COD value are increased in the production. In combination, the input of PAM in the test was 0.2 mg/L.

(III) Influence of settlement time on wastewater

After adding the coagulant under the optimal conditions as described above, a large amount of floc is formed in the wastewater to be settled, and the supernatant is taken for turbidity analysis at different times to prepare a turbidity and static settling time curve. See below:

From this curve, it can be seen that the turbidity removal rate increases slowly with time. From 20 min, the slope of the curve increases greatly, and the turbidity removal rate increases rapidly. After 30 minutes, the curve is almost straight. The turbidity removal rate hardly changed, and here, the standing time after the coagulation was established was 30 min.

(4) Adsorption test

Although the concentration of solid suspended solids and metal ions in the effluent after alum and PAM coagulation is relatively low, about 1 mg/L, the COD content is still relatively high, 390-420 mg/L, which not only fails to meet national emission standards. Moreover, due to the high concentration of residual chemicals in the wastewater, the mineralization index will be affected when returning to use. Therefore, the effluent after coagulation and sedimentation must be further processed before being discharged or returned to the beneficiation process. This experiment focused on the treatment effect of using activated carbon as adsorbent. The coagulated water was added to different types and different amounts of activated carbon, and slowly stirred (100r/min) for 30 min. The test results are shown in Table 4.

Amount of activated carbon (mg/L)

Granular activated carbon

Powdered activated carbon

COD (mg/L)

Pb(mg/L)

Foaming

COD (mg/L)

Pb(mg/L)

Foaming

0

350

1.00

Strong

340

1.00

Strong

50

310

1.00

Strong

260

0.95

Strong

100

250

0.96

Strong

200

0.82

in

150

190

0.90

in

180

0.79

weak

200

175

0.74

weak

160

0.78

weak

It can be seen from Table 4 that with the increase of the amount of activated carbon, the organic matter content in the water is greatly reduced. After the adsorption of activated carbon, the wastewater is slightly higher than the COD, and the rest basically meets the national emission standard. It is evenly distributed in the solution, and has a large adsorption surface area. The adsorption effect is better than that of granular activated carbon, especially for the foaming agent in the liquid, so that the foaming property is significantly reduced, and the amount of the foaming can be seen. Out, to achieve the same defoaming effect, the amount of powdered activated carbon is less than the amount of granular activated carbon, and the optimum amount of the mass fraction is 50× 10-6 .

Third, the conclusion

The ore dressing wastewater is coagulated and precipitated by alum (30mg/L) and PAM (O.2mg/L), and then purified by powdered activated carbon (50mg/L) to meet the national industrial wastewater discharge standard. The process is simple and effective. Has a wide range of industrial applications.

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