CN104445717A - Synchronous fluorine-calcium removal treatment process for reverse osmosis concentrated liquor of waste water from lead-zinc smelting - Google Patents

Abstract

The invention relates to a process for synchronous defluoridation and decalcification of lead-zinc smelting wastewater by reverse osmosis concentrated liquid. The process steps are firstly oxidative precipitation to defluoride, then precipitation to decalcify, then adsorption to defluoride, and then active oxidation Aluminum regeneration, defluorination of the regeneration mixture, decalcification of the regeneration mixture, treatment of the regeneration mixture, and finally precipitation and defluorination. The precipitated sludge generated during the decalcification process is collected and dehydrated by pressure filtration. The water is returned to the reverse osmosis concentrate collection tank for recycling treatment, and the mud cake is treated uniformly. By adopting oxidation, precipitation, and adsorption treatment processes, the fluorine and calcium contents of the reverse osmosis concentrate are lower than 3 mg/L and 50 mg/L respectively, which solves the problem of fluoride and calcium ions in the subsequent evaporation and concentration of the reverse osmosis concentrate. Scale, clogging problem.

Description

A process for simultaneous removal of fluoride and calcium from lead-zinc smelting wastewater by reverse osmosis concentrate

technical field

The invention belongs to the technical field of industrial wastewater treatment, and relates to a process for synchronously removing fluoride and calcium from lead-zinc smelting wastewater by reverse osmosis concentrated liquid.

Background technique

In recent years, my country has entered a period of high incidence of heavy metal pollution incidents, and incidents of children's blood lead exceeding the standard have occurred in many places, especially accidental discharges from mines and smelting enterprises, which have caused serious ecological environmental pollution. Lead and zinc smelting is a highly polluting industry in the non-ferrous metal industry, and the discharge of wastewater containing heavy metal pollutants poses a serious threat to the safety of the ecological environment. The water quality of lead-zinc smelting wastewater is complex, and its main pollutants include heavy metal ions lead, zinc, cadmium, chromium, cobalt, nickel, copper, arsenic, fluoride, chloride, etc., which are generally acidic. With the continuous improvement of my country's environmental protection requirements and the depletion of water resources, the advanced treatment, reuse and zero discharge of lead-zinc smelting wastewater have received more and more attention.

In 2010, Zhongjin Lingnan Shaoguan Smelter decided to implement zero-discharge treatment of smelting wastewater. On the basis of the original wastewater treatment facilities, reverse osmosis concentration of nanofiltration concentrated water and evaporation crystallization of reverse osmosis concentrated liquid were added, reverse osmosis water production and evaporation condensation The water has reached the water quality standard of tap water, and all of it is reused for production, realizing zero discharge and full reuse of wastewater. After the zero discharge system of Shaoguan Smelter is completed, the wastewater treatment process is chemical precipitation + ultrafiltration + nanofiltration + reverse osmosis + MVR evaporation. Since the wastewater contains a certain amount of fluoride ions and a large amount of calcium ions and sulfate ions, it is treated by membrane After the process is concentrated, the fluoride ion, calcium ion and sulfate ion content in the reverse osmosis concentrate can reach 30-50 mg/L, 1000-2000 mg/L and 8000-10000 mg/L respectively. During the operation of the system, the MVR evaporates The device was severely fouled and blocked, and the chemical cleaning effect was poor, so it could only be cleaned physically with a high-pressure water gun, which was extremely difficult to clean. The composition analysis of scales shows that it contains a large amount of CaF ₂ and CaSO ₄ . Therefore, the removal of fluoride ions and calcium ions in reverse osmosis concentrate is very important to solve the fouling and blockage of subsequent evaporation equipment and ensure its stable operation.

Different from conventional industrial wastewater, in order to avoid fouling of reverse osmosis membranes due to fluoride ions and calcium ions, a large amount of high-performance scale inhibitors are added during the operation of reverse osmosis equipment. The content is high, but it is difficult to precipitate naturally or the natural precipitation process is extremely slow, so the traditional precipitation and adsorption process cannot be simply used to remove fluoride, and the molecular structure of the scale inhibitor in the reverse osmosis concentrate must be destroyed first, so as to facilitate the interaction between fluoride ions and calcium The ions react to form calcium fluoride precipitates. Research reports and actual operation experience show that the conventional calcium precipitation defluorination process can reduce the fluoride ion concentration to 8-10 mg/L, while the activated alumina adsorption treatment process can reduce the fluoride ion concentration to 1-3 mg/L. Therefore, the removal of fluoride ions in the reverse osmosis concentrate of lead-zinc smelting wastewater must be combined with water quality characteristics. On the other hand, the content of sulfate ions in the reverse osmosis concentrate is extremely high. The current evaporation and concentration process has not solved the problem of calcium ion scaling well. During the evaporation process, it is easy to form CaSO ₄ precipitates and cause scaling and blockage. The simultaneous removal of calcium ions during the process is also extremely important.

Contents of the invention

In order to overcome the above-mentioned technical shortcomings, the present invention provides a simultaneous defluoridation and calcium removal treatment process for reverse osmosis concentrated liquid of lead-zinc smelting wastewater, which can efficiently remove fluoride ions and calcium ions in lead-zinc smelting wastewater. Provide technical support for the stable operation of the liquid evaporation concentration crystallization system and the realization of zero discharge and full reuse of lead-zinc smelting wastewater .

The technical method adopted by the present invention to solve the technical problem is: a process for synchronous defluoridation and decalcification of lead-zinc smelting wastewater reverse osmosis concentrate, and its process steps are:

Step 1: Oxidative precipitation to remove fluoride, first add H ₂ O ₂ with a mass concentration of 10% to the reverse osmosis concentrate, the dosage is 200 mg/L, and the oxidation reaction time is 30 min, so as to destroy the antiscalant molecules against the reverse osmosis Scale inhibition effect of fluoride ions and calcium ions in the permeate concentrate; then adjust the pH value to 8.5-9.0 with 10% NaOH solution, and add PFS and PAM at concentrations of 30 mg/L and 5 mg/L respectively , after fully stirring the reaction, let it settle for 3 hours to obtain a supernatant, and the fluoride ion concentration in the supernatant is lower than 10 mg/L;

Step 2: Precipitate and remove calcium, add Na ₂ CO ₃ solution with a mass concentration of 20% to the supernatant produced in Step 1 according to 1.2 times the molar concentration of calcium ions in the reverse osmosis concentrate, and then add 5 mg/L PAM, after fully stirring the reaction, let it settle for 3 h to obtain a supernatant, the calcium ion concentration in the supernatant is lower than 50 mg/L;

Step 3: Adsorption to remove fluorine, take the supernatant obtained in step 2, and undergo two-stage activated alumina adsorption treatment. The adsorbent is granular α-Al ₂ O ₃ , with a particle size of 2-3 mm and a saturated adsorption capacity of 2.0 kg/t, after the two-stage adsorption treatment, the fluoride ion concentration in the reverse osmosis concentrate is lower than 3mg/L, and then enters the evaporation concentration system for the next step of treatment;

Step 4: Regeneration of activated alumina. After the activated alumina described in step 3 is saturated, reverse osmosis water is used as backwash water for backwashing. The backwashing time is 15 minutes, and then 3% aluminum sulfate solution is used as regeneration solution. Pump into the activated alumina filter material layer, regenerate for 1.0 h, rinse with reverse osmosis water after regeneration, and rinse for 0.5 h, and the generated backwash waste liquid, regeneration waste liquid and leaching waste liquid are mixed and collected as regeneration mixture liquid;

Step 5: Remove fluoride from the regeneration mixed solution, add Ca(OH) ₂ solution with a mass concentration of 10% to the regeneration mixed solution at 2.5 times the molar concentration of fluoride ions, and at the same time, use a concentration of 30 mg/L and 5 mg/L Add PFS and PAM respectively, fully stir the reaction, let it settle for 3 hours, and then the fluoride ion concentration in the regeneration mixture is lower than 10 mg/L;

Step 6: Calcium removal in the regeneration mixed solution, add Na ₂ CO ₃ solution with a mass concentration of 20% to the regeneration mixed solution obtained in step 5 at 1.2 times the molar concentration of calcium ions, and add 5 mg/L at the same time For PAM, the concentration of calcium ions in the regenerated mixed solution is lower than 50 mg/L after the reaction is fully stirred and allowed to settle for 3 hours;

Step 7: Treatment of the regenerated mixed liquor, the regenerated mixed liquor treated in steps 5 and 6 enters the nanofiltration system together with the original lead-zinc smelting wastewater;

Step 8: Precipitation and defluoridation. The precipitated sludge generated during the decalcification process is collected and dehydrated by pressure filtration. The pressure filtration water is returned to the reverse osmosis concentrated liquid collection tank for recycling treatment, and the mud cake is uniformly processed.

The total amount of the regeneration mixture in step 4 is 8% of the total treatment capacity of the reverse osmosis dope in one regeneration cycle.

The beneficial effects of the present invention are: for the adverse effect of the scale inhibitor in the reverse _osmosis dope on the reaction precipitation of fluoride ion and calcium ion, _H2O2 is used as the oxidant to destroy the scale inhibition effect of the scale inhibitor in the reverse osmosis dope, Ensure the reaction precipitation effect of fluoride ion and calcium ion; through the two-stage activated alumina adsorption and defluorination treatment process for the reverse osmosis concentrate after defluoridation and calcium removal by precipitation, ensure that the fluoride ion concentration in the reverse osmosis concentrate is lower than 3 mg/ L; by sequentially adding Ca(OH) ₂ , PFS, PAM, Na2CO3 and other precipitants to the regeneration mixed solution produced during the regeneration process of activated alumina to ensure that the concentration of fluoride ion and calcium ion in the regeneration mixed solution is lower than 3 mg/ L and 50 mg/L, and then enter the nanofiltration treatment system together with the lead-zinc smelting wastewater for the next step of treatment, without generating new effluent wastewater, to ensure the realization of zero discharge of wastewater; The fluorine and calcium contents of the permeate concentrate are lower than 3 mg/L and 50 mg/L respectively, which solves the problem of scaling and blockage caused by fluorine and calcium ions in the subsequent evaporation and concentration process of the reverse osmosis concentrate.

Description of drawings

Fig. 1 is a block diagram of the present invention;

Fig. 2 is a schematic structural diagram of an embodiment of the present invention.

In Figure 2: 1-reverse osmosis concentrated liquid storage tank, 2-oxidation tank, 3-defluorination precipitation tank, 4-decalcification precipitation tank, 5-intermediate storage tank, 6-sand filter tank, 7-sand filter storage tank , 8-first-level adsorption tank, 9-secondary adsorption tank, 13-regenerated mixed solution pool, 14-regenerated mixed solution defluoridation and precipitation tank, 15-regenerated mixed solution decalcification and precipitation tank, 16-sludge concentration tank.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Referring to Fig. 1, a reverse osmosis concentrated liquid synchronous defluoridation and decalcification treatment process of lead-zinc smelting wastewater, the process steps are:

Step 1: Oxidative precipitation to remove fluoride, first add H ₂ O ₂ with a mass concentration of 10% to the reverse osmosis concentrate, the dosage is 200 mg/L, and the oxidation reaction time is 30 min, so as to destroy the antiscalant molecules against the reverse osmosis Scale inhibition effect of fluoride ions and calcium ions in the permeate concentrate; then adjust the pH value to 8.5-9.0 with 10% NaOH solution, and add PFS and PAM at concentrations of 30 mg/L and 5 mg/L respectively , after fully stirring the reaction, let it settle for 3 hours to obtain a supernatant, and the fluoride ion concentration in the supernatant is lower than 10 mg/L;

Step 2: Precipitate and remove calcium, add Na ₂ CO ₃ solution with a mass concentration of 20% to the supernatant produced in Step 1 according to 1.2 times the molar concentration of calcium ions in the reverse osmosis concentrate, and then add 5 mg/L PAM, after fully stirring the reaction, let it settle for 3 h to obtain a supernatant, the calcium ion concentration in the supernatant is lower than 50 mg/L;

Step 3: Adsorption to remove fluorine, take the supernatant obtained in step 2, and undergo two-stage activated alumina adsorption treatment. The adsorbent is granular α-Al ₂ O ₃ , with a particle size of 2-3 mm and a saturated adsorption capacity of 2.0 kg/t, after the two-stage adsorption treatment, the fluoride ion concentration in the reverse osmosis concentrate is lower than 3mg/L, and then enters the evaporation concentration system for the next step of treatment;

Step 4: Regeneration of activated alumina. After the activated alumina described in step 3 is saturated, reverse osmosis water is used as backwash water for backwashing. The backwashing time is 15 minutes, and then 3% aluminum sulfate solution is used as regeneration solution. Pump into the activated alumina filter material layer, regenerate for 1.0 h, rinse with reverse osmosis water after regeneration, and rinse for 0.5 h, and the generated backwash waste liquid, regeneration waste liquid and leaching waste liquid are mixed and collected as regeneration mixture liquid, the total amount of regeneration mixed liquid is 8% of the total treatment capacity of reverse osmosis concentrated liquid in a regeneration cycle;

Step 5: Remove fluoride from the regeneration mixed solution, add Ca(OH) ₂ solution with a mass concentration of 10% to the regeneration mixed solution at 2.5 times the molar concentration of fluoride ions, and at the same time, use a concentration of 30 mg/L and 5 mg/L Add PFS and PAM respectively, fully stir the reaction, let it settle for 3 hours, and then the fluoride ion concentration in the regeneration mixture is lower than 10 mg/L;

Step 6: Calcium removal in the regeneration mixed solution, add Na ₂ CO ₃ solution with a mass concentration of 20% to the regeneration mixed solution obtained in step 5 at 1.2 times the molar concentration of calcium ions, and add 5 mg/L at the same time For PAM, the concentration of calcium ions in the regenerated mixed solution is lower than 50 mg/L after the reaction is fully stirred and allowed to settle for 3 hours;

Step 7: Treatment of the regenerated mixed liquor, the regenerated mixed liquor treated in steps 5 and 6 enters the nanofiltration system together with the original lead-zinc smelting wastewater;

Step 8: Precipitation and defluoridation. The precipitated sludge generated during the decalcification process is collected and dehydrated by pressure filtration. The pressure filtration water is returned to the reverse osmosis concentrated liquid collection tank for recycling treatment, and the mud cake is uniformly processed.

Example: The reverse osmosis dope produced during the zero-discharge treatment process of lead-zinc smelting wastewater in a smelter is treated continuously according to the process flow of the present invention, and the treatment scale is 5 m ³ /h. See Figure 2 for its working steps as follows:

Step 1: Continuously pump the reverse osmosis concentrated liquid from the reverse osmosis concentrated liquid storage tank 1 into the oxidation tank 2 at a flow rate of 5 m ³ /h, and continuously add 10% H ₂ O ₂ to the oxidation tank 2 at a flow rate of 10 L/h , the effluent from the oxidation tank 2 flows into the fluorine-removing precipitation tank 3 by itself, and the fluoride-removing precipitation tank is a vertical flow sedimentation tank with a central cylinder, and the pH value is adjusted to 8.5-9.0 with a NaOH solution with a mass concentration of 10%, and the pH value is adjusted to 30 mg/L respectively Add PFS and PAM at a concentration of 5 mg/L;

Step 2: The effluent from the fluorine-removing precipitation tank 3 flows into the calcium-removing precipitation tank 4 by itself, and the Na ₂ CO ₃ solution with a mass concentration of 20% is added according to 1.2 times the molar concentration of calcium ions in the reverse osmosis concentrate, and an additional 5 mg/ L of PAM, the decalcification sedimentation tank 4 outlet water enters the intermediate storage tank 5;

Step 3: Continuously pump the reverse osmosis concentrated liquid into the sand filter tank 6 from the intermediate storage tank 5 at a flow rate of 5 m ³ /h, and the water from the sand filter tank enters the sand filter storage tank 7, and then pumps it into the primary adsorption tank 8 And the secondary adsorption tank 9, the adsorption treatment effluent enters the effluent pool 10 for storage to be treated by evaporation and concentration in the next step;

Step 4: After the fluorine ion content in the adsorption treatment water exceeds 3 mg/L, the activated alumina in the adsorption tanks 8 and 9 must be regenerated. During regeneration, the filter layer is firstly backwashed, and the reverse osmosis water is used as backwashing Water source, the expansion rate of the filter layer is 30% to 50%, the backwash time is 15min, and the flushing intensity is 12 L/m ² ·s. The configured 3% aluminum sulfate solution is pumped into the adsorption tanks 8 and 9, the flow rate is 3-5m/h, and the regeneration time is 1.0 h, and the generated fluorine-containing regeneration waste liquid enters the regeneration mixed liquid pool 13; Activated alumina is leached, using reverse osmosis water as the leaching water source, and rinsing the adsorption tank for 0.5 h at a flow rate of 2.5 m ³ /h, and the resulting leaching waste liquid enters the regeneration mixed solution pool 13 to complete the activated alumina regeneration treatment;

Step 5: The backwash waste liquid, regeneration waste liquid and leaching waste liquid produced in the activated alumina regeneration process are stored in the regeneration mixed liquid pool 13, which mainly contains a large amount of fluorine ions and a certain amount of suspended matter, and are pumped into the regeneration Mixed liquid defluoridation precipitation tank 14, add Ca(OH) ₂ solution with a mass concentration of 10% according to 2.5 times the molar concentration of fluoride ions, and simultaneously add PFS and PAM at concentrations of 30 mg/L and 5 mg/L , the effluent of the regenerated mixed solution defluoridation precipitation tank 14 enters the regenerated mixed solution decalcification precipitation tank 15, and the Na ₂ CO ₃ solution with a mass concentration of 20% is added according to 1.2 times the molar concentration of calcium ions, and at the same time the concentration is 5 mg/L Add PAM to react and precipitate, and the concentration of fluoride ion and calcium ion in the effluent of regeneration mixed solution decalcification and precipitation tank 15 is lower than 10 mg/L and 50 mg/L respectively, and directly enters the nanofiltration device of the original wastewater treatment system for further concentration treatment;

Step 6: The precipitated sludge generated during the process of sedimentation, defluoridation and calcium removal of the reverse osmosis concentrated solution and regeneration mixed solution is regularly discharged into the sludge thickening tank 16, further concentrated and dehydrated by pressure filtration, the mud cake is uniformly processed, and the pressure filtration water is returned to the sludge concentration tank 16. Permeate concentrated liquid storage tank 1.

The main equipment performance parameters in the above process steps are shown in Table 1. When the system is running, samples are taken and analyzed every 12 hours, and the treatment effect is shown in Table 2:

Table 1 Main equipment and parameters of reverse osmosis dope synchronous defluoridation and calcium removal system

Table 2 Treatment effect

The above table shows that the present invention aims at the adverse effect _of the scale inhibitor in the reverse osmosis dope on the reaction precipitation of fluoride and calcium ions, and uses _H2O2 as an oxidant to destroy the scale inhibitor in the reverse osmosis dope to ensure that Fluoride ion and calcium ion reaction precipitation effect; by adopting two-stage activated alumina adsorption and defluorination treatment process for the reverse osmosis concentrate after defluoridation and calcium removal by precipitation, to ensure that the concentration of fluoride ion in the reverse osmosis concentrate is lower than 3 mg/L ;The regeneration mixed solution produced by the activated alumina regeneration process is sequentially added with Ca(OH) ₂ , PFS, PAM, Na2CO3 and other precipitants to ensure that the concentration of fluoride ion and calcium ion in the regeneration mixed solution is lower than 3 mg/L respectively and 50 mg/L, and then enter the nanofiltration treatment system together with the lead-zinc smelting wastewater for the next step of treatment, without generating new effluent wastewater, to ensure the realization of zero discharge of wastewater; through the use of oxidation, precipitation, and adsorption treatment processes followed by reverse osmosis The fluorine and calcium contents of the concentrated liquid are respectively lower than 3 mg/L and 50 mg/L, which solves the problem of scaling and blockage caused by fluorine and calcium ions in the subsequent evaporation and concentration process of the reverse osmosis concentrated liquid.

Claims (2)

1. A reverse osmosis dope synchronous defluoridation and decalcification treatment process for lead-zinc smelting wastewater, characterized in that the process steps are: Step 1: Oxidative precipitation to remove fluoride, first add H ₂ O ₂ with a mass concentration of 10% to the reverse osmosis concentrate, the dosage is 200 mg/L, and the oxidation reaction time is 30 min, so as to destroy the antiscalant molecules against the reverse osmosis Scale inhibition effect of fluoride ions and calcium ions in the permeate concentrate; then adjust the pH value to 8.5-9.0 with 10% NaOH solution, and add PFS and PAM at concentrations of 30 mg/L and 5 mg/L respectively , after fully stirring the reaction, let it settle for 3 hours to obtain a supernatant, and the fluoride ion concentration in the supernatant is lower than 10 mg/L; Step 2: Precipitate and remove calcium, add Na ₂ CO ₃ solution with a mass concentration of 20% to the supernatant produced in Step 1 according to 1.2 times the molar concentration of calcium ions in the reverse osmosis concentrate, and then add 5 mg/L PAM, after fully stirring the reaction, let it settle for 3 h to obtain a supernatant, the calcium ion concentration in the supernatant is lower than 50 mg/L; Step 3: Adsorption to remove fluorine, take the supernatant obtained in step 2, and undergo two-stage activated alumina adsorption treatment. The adsorbent is granular α-Al ₂ O ₃ , with a particle size of 2-3 mm and a saturated adsorption capacity of 2.0 kg/t, after the two-stage adsorption treatment, the fluoride ion concentration in the reverse osmosis concentrate is lower than 3mg/L, and then enters the evaporation concentration system for the next step of treatment; Step 4: Regeneration of activated alumina. After the activated alumina described in step 3 is saturated, reverse osmosis water is used as backwash water for backwashing. The backwashing time is 15 minutes, and then 3% aluminum sulfate solution is used as regeneration solution. Pump into the activated alumina filter material layer, regenerate for 1.0 h, rinse with reverse osmosis water after regeneration, and rinse for 0.5 h, and the generated backwash waste liquid, regeneration waste liquid and leaching waste liquid are mixed and collected as regeneration mixture liquid; Step 5: Remove fluoride from the regeneration mixed solution, add Ca(OH) ₂ solution with a mass concentration of 10% to the regeneration mixed solution at 2.5 times the molar concentration of fluoride ions, and at the same time, use a concentration of 30 mg/L and 5 mg/L Add PFS and PAM respectively, fully stir the reaction, let it settle for 3 hours, and then the fluoride ion concentration in the regeneration mixture is lower than 10 mg/L; Step 6: Calcium removal in the regeneration mixed solution, add Na ₂ CO ₃ solution with a mass concentration of 20% to the regeneration mixed solution obtained in step 5 at 1.2 times the molar concentration of calcium ions, and add 5 mg/L at the same time For PAM, the concentration of calcium ions in the regenerated mixed solution is lower than 50 mg/L after the reaction is fully stirred and allowed to settle for 3 hours; Step 7: Treatment of the regenerated mixed liquor, the regenerated mixed liquor treated in steps 5 and 6 enters the nanofiltration system together with the original lead-zinc smelting wastewater; Step 8: Precipitation and defluoridation. The precipitated sludge generated during the decalcification process is collected and dehydrated by pressure filtration. The pressure filtration water is returned to the reverse osmosis concentrated liquid collection tank for recycling treatment, and the mud cake is uniformly processed. 2. The reverse osmosis concentrated liquid simultaneous defluoridation and calcium removal process for lead-zinc smelting wastewater, characterized in that the total amount of the regeneration mixed liquid in step 4 is 8% of the total treatment capacity of the reverse osmosis concentrated liquid in one regeneration cycle.