I. Introduction
Our company's ore dressing wastewater has a large daily discharge. The wastewater flows into the tailings pond through the pipeline and the overflow water is discharged directly into the downstream water system. The tungsten ore beneficiation wastewater contains a large amount of suspended solids, which is difficult to settle for a long time and has a high pH. If it is discharged without treatment, it will have a great impact on the surrounding environment, and it is necessary to seek a cost-effective treatment method. Under the arrangement and guiding the company to the sum of the Quality Control Department Zhou, we tested a calcium chloride - polymerization process wastewater treatment tailings flocculation of aluminum chloride.
Second, wastewater quality
Static test
Take a 100mL measuring cylinder filled with waste water, start timing when the scale is full, observe the phenomenon of water standing sedimentation. When the time was 5, 10, 20, 30, 40, 50, 60, 70, 80 minutes, the turbidity of the solution was observed from the supernatant. It can be seen from the experimental phenomenon that since the wastewater exhibits the physicochemical properties of the colloid, there is almost no sedimentation effect without adding any treatment agent, and the sedimentation rate is extremely slow.
Due to the addition of sodium silicate (a strong dispersant) in the beneficiation, the fine particles in the slurry form a very stable colloidal suspension dispersion. Under natural conditions, even if it is left for half a month, the wastewater will not clarify. The appearance of the wastewater is rice soup color and turbid. After treatment, the wastewater can reach the secondary standard of comprehensive wastewater discharge standard (GB8978-1996).
Third, the current processing method
At present, our company's wastewater treatment uses the stability of lime to destroy suspended solids, and finally neutralizes the pH with sulfuric acid to meet emission requirements. The calcium ion provided by this method can achieve the destabilization effect well, but the sedimentation speed is not very fast, and there are many suspended solids that need to settle in the tailings pond, and at the same time, the alkalinity of the wastewater increases, and then the sulfuric acid is lowered to lower the pH. The value will make the solution turbid, and it will be better to adjust the pH with sulfuric acid after draining outside the tailings pond.
Fourth, the choice of destabilizer
The particles of the tailings slurry colloid are in a state of uniform suspension without being destroyed, and have stability. The colloid is dispersed by small particles, and the diffusion effect generated by Brownian motion can resist sedimentation and have sedimentation stability. If the effect of adding flocculant directly to the tailings slurry is not obvious, it will not destroy the silicic acid. We tested the strengthening of acid, weak acid (sulfuric acid), strong electrolytes, strong alkali can achieve the effect of destroying the stability of silicic acid, but the acid should adjust the acidity of the wastewater to pH ≈1 to precipitate the suspended matter, and the clear liquid is still More turbid, and finally adjust PH6 ~ 9, in order to meet the discharge standards; strengthen the electrolyte (strong acid and alkali salt PH almost neutral), can destroy the silicic acid without adjusting the PH value. Ferrous sulfate, ferrous chloride can quickly precipitate, but more than two hours the supernatant solution is placed in a ferrous ion will gradually oxidized by oxygen and significantly tan ferric ions reach emission chromaticity Claim. Calcium chloride can quickly settle the suspended solids, and finally add some coagulant to accelerate the sedimentation rate, and settle some fine particles to discharge directly. Therefore, calcium chloride is used as a destabilizing agent.
Fifth, the choice of flocculant
Take a set of 100mL tailings slurry, add a certain amount of calcium chloride, then add polyacrylamide, gelatin, polyaluminum chloride separately, stir, observe the phenomenon, as shown in Table 1.
Table 1 Flocculant selection
Flocculant category | Precipitation rate | Supernatant brightness | Experimental phenomena |
Polyacrylamide gelatin Polyaluminum chloride | quickly SLOW Faster | Very bright Brighter Very bright | A large floc is formed within 5 seconds, and the sedimentation process is completed after 1 minute, and the supernatant is clear. A fine precipitate formed within 2 minutes, and the sedimentation process was completed after 15 minutes. The supernatant was turbid. Large flocs are formed within 15 seconds, the sedimentation process is completed within 3 minutes, and the supernatant is clear. |
Since polyacrylamide is an organic flocculant and the price is more than ten times that of polyaluminum chloride, and the polyaluminum chloride is weakly acidic, and the alkalinity of the tailings pulp wastewater can be adjusted, the polyaluminum chloride is selected as a flocculant. Polymerized aluminum trichloride is a polymer coagulant, which is formed by the bridging action of hydroxide ions and the polymerization of polyvalent anions to form an inorganic polymer water treatment agent with a large molecular weight and a high charge. The water has a wide pH value and can be agglomerated in the range of pH 5.0 to 9.0. The best effect is pH 6.5 to 7.5.
Six, conditional choice
(1) Selection of calcium chloride dosage
Consulted the mineral processing capacity of our company's mineral processing technicians , the approximate relationship between water quantity and dosage, and calculated the theoretical dosage of calcium chloride.
1 ton of raw ore - 4 tons of water - 7kg of sodium silicate - 4.48kg of silicic acid
The concentration of silicic acid in the wastewater was 1.12 g/L.
The reaction formula and calculation are as follows:
Na 2 SiO 3 +2H 2 O=H 2 SiO 3 +2NaOH
H 2 SiO 3 +CaCl 2 =CaSiO 3 +2HCl
Na 2 SiO 3 —H 2 SiO 3 —CaCl 2 —Ca SiO 3
122 78 75.5
7 4.48
It shows that 4 tons of wastewater from 1 ton of raw ore contains 4.48 kg of silicic acid, which means that the concentration of silicic acid in the wastewater is 1.12 g/L.
H 2 SiO 3 —CaCl 2
78 75.5
1.12 X
X=1.08g
Theoretically, it takes 1.08 g of calcium chloride to treat 1 L of wastewater.
Take 4 25mL tailings slurry and add 10.8mg, 16.2mg, 21.6mg, 27.0mg of calcium chloride and the same amount of polyaluminium chloride for the experiment. Since no turbidity meter is used for visual observation, the results are shown in the table. 2 is shown.
Table 2 Effect of different amounts of destabilizer
Calcium chloride dosage (mg) | Time required to settle 60% (minutes) | Clearance brightness (visual observation) | Clear pH |
10.8 16.2 21.6 27.0 | twenty two twenty four 25 33 | Microturbid Clear Clear Clear | 7.34 7.35 7.30 7.36 |
From the brightness and economics of the clear solution, it was decided to treat one ton of water with 16.2 mg/25 mL, ie 648 g of calcium chloride.
(2) Selection of flocculant dosage
Take 4 25mL tailings slurry, add 16.2mg calcium chloride and polyaluminum chloride 0.0225 mg, 0.0300 mg, 0.0375 mg, 0.0450mg, 0.0525 mg, and stir the experiment. No visual observation is used for the turbidity meter. as shown in Table 3.
Table 3 Effect of different dosages of flocculant
Amount of polyaluminum chloride (g) | Time required to settle 60% (minutes) | Clearance brightness (visual observation) | Clear pH |
0.0225 0.0300 0.0375 0.0450 0.0525 | 11 13 twenty three 25 28 | More turbid Microturbidity Clear Clear Clear | 7.59 7.50 7.43 7.34 7.32 |
Experiments show that the brightness is proportional to the amount of polymerized aluminum trichloride added, and the sedimentation rate is inversely proportional to the amount of polymerized aluminum trichloride added. Considering the dosage, sedimentation speed and brightness of the clear solution, it is decided to use a reasonable amount of 0.0375 g/25mL, that is, 1500g of polyaluminum chloride to treat one ton of water.
7. Economic budget
The approximate price of the currently used agents is shown in Table 4.
Table 4 Current price of various pharmaceuticals in water treatment
Industrial calcium chloride | Polyaluminum chloride | lime | sulfuric acid |
1,200 yuan / ton | 1,200 yuan / ton | 400 yuan / ton | 280 yuan / ton |
Lime (60%)
The treatment of 1L water consumption is 1.38g, and the selection of 1 ton of raw ore requires 4 tons of water, then consumes 5.52kg of lime. Dealing with a ton of ore required capital = 0.00552 * 400 = 2.21 (yuan)
Sulfuric acid (98%)
To treat 1L of water, consume 0.5mL of concentrated sulfuric acid. If 1 ton of raw ore is needed, 4 tons of water is needed. Then 8L of sulfuric acid, ie 3.68kg of sulfuric acid, is needed. Then, the treatment of one ton of ore needs funds = 0.00368*280=1.03 (yuan).
The treatment of wastewater with lime-sulfuric acid requires a treatment of 1 ton of ore and consumes 3.24 yuan (yuan).
Calcium chloride
Treatment of 1L of water consumes 1g of calcium chloride, and the treatment of one ton of ore requires funds = 4.8 (yuan).
Polyaluminum chloride
Treatment of 1L of water consumption 1.5g, processing a ton of raw ore requires funds = 0.006 * 1200 = 7.2 (yuan).
Eight, the conclusion
In view of the problem that the wastewater of our company's tungsten tailings pond contains a large amount of water glass, which makes the suspended solids difficult to settle, the treatment of tailings wastewater by calcium chloride-polyaluminum chloride flocculation method destroys the colloidal stability of the wastewater, and then passes the flocculant. Flocculation adsorption removes residual suspended solids and other impurities in wastewater, and accelerates the sedimentation rate. The test results have certain reference value for industrial wastewater treatment and can be used for further industrial experiments.
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