Ping Jiang Huang Jindong Mining Co. Ltd. is a mining dressing and smelting joint venture, the company mainly produces mineral processing waste water as waste water daily emissions of about 1000t. The waste water is discharged into the tailings reservoir through the tailings transfer pump, and the overflow water is directly discharged. Due to the high content of suspended solids in raw water, and the use of mineral processing agents containing water glass and other dispersions in the beneficiation process, the suspended solids exceeded 20 times, and the arsenic exceeded 5 times, causing great damage to the environment. 2004 In the year, it was included in the deadline management project by the provincial environmental protection bureau. Entrusted by the company, Hunan Nonferrous Metal Research Institute conducted a treatment test on the ore dressing wastewater of the company, and determined that the beneficiation wastewater treatment process was first colloidal destabilization and then flocculation sedimentation, and industrial application design was carried out. The project was completed in August 2004 and monitored by the local environmental monitoring department. The main pollutants in the effluent were pH<9, SS<50 and As<0.1mg/L, and the wastewater was discharged.
First, the test part
(1) Wastewater quality
The results of wastewater quality monitoring before treatment are listed in Table 1. The wastewater is overflowing water from the tailings pond. Due to the addition of sodium silicate (a strong dispersing agent) during the beneficiation process, the fine dust in the slurry forms a very stable colloidal dispersion, even in the natural state. The wastewater will not be clarified for a month. The appearance of the wastewater is rice soup and turbid, and its main pollution factors are SS, As, COD, especially SS and As. The treated wastewater is required to meet the first-class standard of the comprehensive wastewater discharge standard GB8978-1996.
(two) test principle
The colloidal particles are in a state of uniform suspension and are not destroyed and have stability. Due to the small size of the dispersed particles, the diffusion of Brownian motion can resist sedimentation and have sedimentation stability. However, since the colloid is a multiphase dispersion system, it has a broad interphase interface and a large free energy, and its fine particles tend to combine with each other into a coarse aggregate, and thus have polymerization instability.
The wastewater from the tailings pond contains a large amount of suspended solids that are difficult to settle and have the physicochemical properties of the colloid. The treatment of this wastewater is first considered to remove the suspended solids from the steady state by adding acid, alkali or a strong electrolyte (usually using lime milk). The As in the wastewater can form insoluble compounds with various metals, and the reaction to form the insoluble compounds is mostly carried out at a higher pH. Therefore, by adding lime milk, the colloidal stability of the wastewater can be achieved, and at the same time It can precipitate and remove arsenic from wastewater, and then flocculate and adsorb by flocculating agent and mesh capture of particulate arsenic to remove suspended solids and other impurities in wastewater. The reaction formula of lime in removing arsenic is as follows:
Ca(OH) 2 +2H 3 AsO 3 ----Ca(AsO 2 ) 2 +4H 2 O
(3) Test methods
First, a certain amount of lime milk was added to the test water to control different pH values ​​of the reaction, and the reaction was carried out under the same stirring condition (120 r/min) for 10 min, and then left to stand for 30 min. The coagulation test was carried out on a six-coagulation mixer, and the amount of water was 1000 mL. The coagulation condition was firstly stirred at 250r/min for 2min, then slowly stirred at 60r/min for 10min, then settled for a period of time. The supernatant was taken at 2cm from the liquid surface by siphon method to analyze the corresponding indicators. Determine the optimum pH and flocculant dosage. Aluminum chloride polymerization with good coagulation performance, alum generated a large, low dosage, high efficiency, the advantages of rapid sedimentation. Therefore, the flocculant is tested using polyaluminum.
(4) Test results
The optimum reaction pH should be determined by experiments to be ≥11, and the test results are listed in Table 2 and Table 3, respectively.
It can be seen from the test results that the flocculated slag is relatively easy to settle. Due to the high SS content of raw water, the floc in the wastewater settled rapidly after 5 minutes of reaction with lime and flocculant. The sedimentation speed in the first 15min was faster, and the As and SS contents decreased rapidly. After 20wan, the sedimentation rate slowed down. It belongs to deceleration and settlement; after 60min, it enters the compression and sedimentation stage, the slag-water ratio is 1:3, and the slag-water ratio is 1:6 after 2h.
Second, the engineering part
(1) Design plan
According to the test results, combined with the actual situation of the enterprise, the design case is as follows:
1. The wastewater treatment project is located on the left side of the secondary pumping station of the current tailings. Considering the expansion of the company's scale, the designed wastewater treatment capacity is 1500m 3 /d.
2. The overflow water of the tailings reservoir is transported through the pipeline to the inlet of the baffle baffle reaction tank, while adding lime milk and controlling the pH value ≥11.0. Then, a flocculant PAC was added in an amount of 20 mg/L. After the flocculation reaction is carried out in the separator reaction tank, the solid-liquid separation is carried out through the water distribution hole from the flow slanting plate sedimentation tank.
3. The sloping plate sedimentation tank is designed with a surface load of q=1.54m 3 /m 2 •h, and the wastewater residence time is 2h. The supernatant liquid flows from the overflow water to the outer tank of the clear water tank (pH value <9) or reused to the flue gas desulfurization system for supplementary water.
4. The bottom flow of the sloping plate is collected by the mud drain and flows into the mud pool, and then transported to the existing tailings pond for sediment through the existing tailings pump.
(II) Economic and technical indicators
Wastewater treatment production operating material consumption breakdown is shown in Table 4. The entire project investment is about 300,000 yuan, and the annual operating cost is not more than 60,000 yuan. In October 2004, the local environmental monitoring department conducted an acceptance check on the wastewater treatment facility. The results showed that the main pollution factors SS<50mg/L, As<0.01mg/L, and chromaticity 5.8 were far lower than the comprehensive wastewater discharge standard. ((GB8978-l996) primary standard. The monitoring results are listed in Table 5.
Third, the conclusion
The lime-flocculation sedimentation method is used to treat the ore-containing wastewater with low arsenic content and suspended solids, which has the characteristics of engineering investment, stable and reliable treatment effect, low operating cost and strong operability. It can reach the standard discharge and can be used to treat the purified water. At present, there are some similar mineral processing enterprises in the region, and their wastewater has not been effectively treated. This method has good promotion and application value and social environmental benefits.
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