Electroplating wastewater treatment method containing nickel
The composition of wastewater generated in electroplating process is very complex, among which heavy metal wastewater is the potential harmful wastewater in electroplating industry. Nickel is a heavy metal that can cause cancer [1] and is also a more expensive resource (2 to 4 times more expensive than copper). Nickel electroplating is widely used in electroplating because of its excellent abrasion resistance, corrosion resistance and weldability. A large amount of waste water containing nickel is produced in the process of nickel plating. If nickel wastewater is not treated and discharged arbitrarily, it will not only harm the environment and human health, but also cause the waste of precious metal resources.
The generation and harm of nickel wastewater from electroplating
The nickel plating wastewater mainly comes from the waste solution of plating bath and rinsing water of plating parts in the production process of nickel plating. The amount of waste plating solution is small, but the concentration of nickel ion is very high. The rinsing water of plating parts is the main source of plating wastewater, accounting for more than 80% of the wastewater discharge in the workshop. The amount of rinse water is large, but the nickel ion concentration is much smaller than that of the waste bath. According to table 2 of discharge standards for electroplating pollutants (GB 21900-2008), the maximum mass concentration of total nickel in electroplating wastewater allowed to be discharged into water body is 0.5 mg/L.
Treatment technology of electroplating wastewater containing nickel
According to different principles, the treatment methods of nickel electroplating wastewater can be divided into three categories: chemical method, physicochemical method and biological method.
2.1 chemical method
The traditional chemical precipitation method, the new process ferrite method, and the high efficiency heavy metal chelating precipitation method are used to treat nickel electroplating wastewater. Among them, chemical precipitation method includes hydroxide precipitation method and sulfide precipitation method.
2.1.1 chemical precipitation method
Li jiao [2] in the experimental study of electroplating wastewater treated by chemical precipitation, CaO, CaCl2 and BaCl2 were used to treat nickel plating wastewater. The comparison showed that BaCl2 had the best complexing effect, the highest removal rate of nickel ions and the worst effect of CaCl2. When CaO and BaCl2 are combined to treat nickel plating wastewater, the removal rate of nickel ions can reach more than 99%, and when the removal rate of nickel ions is the same, the usage of BaCl2 is much less than when it treats nickel plating wastewater alone. Lin dexian et al. [3] firstly used Fenton reagent for oxidation, and then used NaClO oxidation to pre-treat nickel containing wastewater with pH of 3-5 and mass concentration of Ni2+ of 100-150 mg/L. Finally, through chemical precipitation treatment, the mass concentration of nickel ions in the final effluent was lower than 0.1mg /L.
The traditional chemical precipitation method has many advantages, such as mature technology, low investment and low treatment cost. Although a large amount of sludge will be generated in the reaction process and even cause secondary pollution, the treatment effect of traditional chemical precipitation method has been continuously improved with the continuous development and application of collateral breaker and heavy metal collector.
2.1.2 ferrite method
In the chemical precipitation process, the relatively new process is ferrite method. FeSO4 can cause various heavy metal ions to form ferrite crystals and precipitate out. The general formula of ferrite is FeO·Fe2O3 [4]. In the wastewater, Ni2+ can occupy the lattice formation of Fe2+ and remove it by co-precipitation. Generally, when n(Ni2+) : n(FeSO4) is 1∶2~1∶3, and the mass concentration of nickel ion in the wastewater is 30~200 mg/L [5], the precipitation particles formed after ferrite treatment are large and easy to separate, and the particles will not be dissolved again. There is no secondary pollution.
Chang junxia et al. [6] studied the technological conditions of treating nickel wastewater by ferrite method. The results showed that under the conditions of pH=9.0, n(Fe2+) : n(Ni2+)=2∶1 and temperature of 70 ℃, the conversion rate of nickel could reach more than 99.0%, and the Ni2+ in wastewater could decrease from 100 mg/L to 0.47 mg/L. Li jinghong et al. [7] studied the process conditions of low concentration nickel wastewater treated by ferrite method at room temperature. The results showed that Na2CO3 was used as the pH regulator, and the best treatment effect was obtained when the pH was 8.5~9.0, n(Fe3+) : n(Fe2+)=1.5∶1, n(Fe2+) : n(Ni2+)=12∶1 and the stirring time was 15 min. The removal rate of nickel reaches more than 98%, and the mass concentration of nickel ion in the treated wastewater reaches less than 0.20mg /L, meeting the national emission standard.
Both Fenton and ferrite processes contain ferrous ions. Jiang honglong et al. [8] used the combined fenton-ferrite process to treat complexing electroplating wastewater containing copper and nickel. Initial results show that the wastewater pH = 3, H2O2 initial mass concentration is 3.33 g/L, m (Fe2 +) : m (H2O2) = 0.1, the optimal Fenton oxidation temperature of 25 ℃ condition, the first 60 min of Fenton wastewater treatment, and adjust the wastewater after precipitation pH = 11, aeration control flow for 25 mL/min, iron and metal ions in waste water quality ratio of 10, the reaction temperature is 50 ℃, aeration for 60 min contact time, under the condition of the nickel ion in waste water removal rate reached 99.94%, The effluent nickel ion mass concentration is 0.33mg /L, which meets the national emission standard. In addition, phase analysis of precipitated sludge shows that the ferrite sediments such as NiFe2O4 and Fe3O4 obtained under the optimal process conditions have no secondary pollution and can be recycled as magnetic materials.
Ferrite treatment of nickel containing electroplating wastewater has the advantages of simple treatment equipment, less investment and recycling of sediment. At present, ferrite process is developing from a single process to a variety of complex processes. It USES its own advantages and combines with other water treatment processes to form a new process, making its treatment of heavy metal wastewater more perfect.
2.1.3 macromolecule chelation precipitation method
In recent years, the addition of heavy metal chelating agent, a new type of precipitant in the traditional chemical precipitation process, has improved the deficiency of the traditional process. Liu cunhai et al. [9] synthesized HMCA, a heavy metal ion chelating agent, and applied HMCA in nickel plating wastewater. When the pH was 6.5~7.5, the removal rate of Ni2+ could reach over 98.5%. The chelating agent has a good ability to capture Ni2+, and the chelating product formed by interaction with Ni2+ has a compact and stable structure. When the mass concentration of metal chelating agent was 3.79 g/L, the minimum mass concentration of Ni2+ was 0.45 mg/L, which significantly improved the treatment effect of nickel plating wastewater. Liu (10) in alkaline conditions such as the next synthesis of a new type which has the function of flocculation, chelating heavy metal chelating agent, PAS, and PAS is used for heavy metal nickel ion chelating experiment, the experimental results show that the 0.6 mL of PAS to 50 mg/L of nickel wastewater removal rate can reach more than 98%, visible PAS for Ni2 + chelating agent is a kind of good.
2.2 physicochemical method
The rise and progress of new physical and chemical technologies and new processes make clean production of electroplating enterprises possible. Adsorption technologies, ion exchange technologies, membrane separation technologies and ion flotation technologies commonly used in the treatment of nickel-containing electroplating wastewater are all new and efficient water treatment technologies developed on the basis of resource recovery.
2.2.1 adsorption technology
Adsorption is an effective method to remove heavy metal ions by using the unique structure of adsorbents. Zeolite, activated carbon, humic acid and so on are often used as adsorbents for treating nickel electroplating wastewater.
The function of artificial zeolite is similar to that of natural zeolite. The maximum adsorption capacity of Ni2+ was 13.03 mg/g [11]. Ulster et al. [12] modified the surface of zeolite with butyldiketoxime (DMG), and used artificial zeolite modified with hexadecyl trimethylammonium bromide (CTAB) to adsorb Ni2+ in simulated wastewater. The results showed that when the solution volume was 25 mL, the initial mass concentration was 20 mg/L, the pH value was 7.0, and the temperature was 35 ℃, the adsorption rate reached more than 98% under the condition of adding mass of modified zeolite was 1.1 g and adsorption time was 50 min, and the influence of other interfering ions (Cu2+, Pb2+) was not significant. Chen eryu [13] studied the effect of new modified zeolite (na-y type) on Ni2+ removal in electroplating wastewater by spectrophotometry. The results showed that, at room temperature and pH=4, when the mass fraction of modified zeolite was 0.4% and the adsorption time was 2 h, the removal rate of Ni2+ in the waste water solution could reach more than 99%. The na-y zeolite could be reused after leaching with HCl and NaCl mixed solutions, and the adsorption capacity decreased after regeneration, but the decrease was not obvious.
Activated carbon can effectively remove complexed nickel ions from wastewater. Qi yanshan et al. [14] studied the adsorption behavior of powdered activated carbon on complexed nickel ions with low mass concentration citric acid in aqueous solution under the static adsorption condition. The test results showed that: when the initial pH of the solution was 11.0 and the mass concentration of activated carbon was 10.0 g/L, the removal rate of nickel ions reached 72.3%.
Dao-cheng luo (15) by using humic acid resin processing heavy metals such as Ni2 + experiment shows that the effluent pH 5.0 ~ 7.0, Ni2 + mass concentration of 50 mg/L, the adsorption of humic acid resin by ion exchange and complexation Ni2 + removal rate can reach more than 98%, and the treated wastewater is close to neutral, Ni2 + in waste water content significantly below the national discharge standard.
At present, the adsorbent widely used in industry is expensive, which restricts the wide application of adsorption technology. At the same time, the regeneration and secondary pollution of adsorbent are also the problems that should be considered in the wastewater treatment process of adsorption technology.
2.2.2 ion exchange technology
With the development of new large-pass ion-exchange resin and ion-exchange continuous process, ion-exchange method as a means of nickel plating rinse water "zero discharge" has aroused the interest of academia.
Hou xingang et al. [16] used ion exchange method to conduct adsorption experiments on low-concentration nickel sulfate solution. The results showed that: at room temperature, the reaction time of 001×8 type strong acid gel cation exchange resin 4.0 g, the mass concentration of nickel ion 1.0 g/L, the reaction time and pH 5~6, the recovery of nickel ion can reach more than 95%. Kinetic studies show that the adsorption rate is mainly controlled by liquid film diffusion. Song jiming et al. [17] compared the adsorption performance of aminophosphoric acid chelating resin and other chelating resins on nickel ions in weakly acidic electroplating wastewater, and concluded that the adsorption capacity of aminophosphoric acid chelating resin on Ni2+ increased by 29.5% after it was converted from H+ to Na+. After treatment, the mass concentration of Ni2+ in water is less than 0.020 mg/L. T. h. Eom et al. [18] adopted ion exchange technology for electroplating wastewater treatment, and the removal rate of Ni2+ could exceed 99%.
By combining ion exchange technology with membrane technology, a new process was developed to treat nickel electroplating wastewater. Wu Hongfeng etc. [19] by ion exchange, ultrafiltration, reverse osmosis composite nickel plating rinse wastewater treatment technology, the system after more than four months after the operation, monitoring results show that nickel plating rinse water Ni2 + mass concentration by 424 mg/L dropped to below 1.0 mg/L, Ni2 + recovery more than 99%, the wastewater powerusageeffectiveness is greater than 60% overall, the system can reuse to nickel plating rinse water tank. The method has the advantages of stable effluent quality and recoverable nickel resources and water resources.
2.2.3 membrane separation technology
Nickel is both a heavy metal and a precious metal. Membrane separation technology can not only remove nickel ions from wastewater, but also realize the recovery and utilization of nickel, so as to achieve the purpose of clean production.
Zhou lijun et al. [20] concentrated and separated the nickel plating rinsing wastewater by the combined process of ultrafiltration and reverse osmosis, and the effluent quality was close to pure water. Hu zifu et al. [21] adopted two-stage RO membrane system to treat the bleaching wastewater containing nickel from 250 to 350 mg/L, and the interception rate of nickel reached more than 99.9%.
With the application of the new nanofiltration membrane, wang xintong et al. [22] separated the plating nickel rinsing water with 99.5% removal rate of nickel ions, which could be discharged directly or reused in the workshop. Li xingyun et al. [23] treated simulated Ni2+ wastewater with a mass concentration of 2 000 mg/L and pH=5.32 by membrane electrolysis. The results show that the H+ produced by the anode reaction is neutralized by OH- in the anode liquid, and the negative film prevents H+ from passing through, thus improving the recovery of nickel. And the current efficiency can be up to more than 90%, which is 30% higher than the ordinary electrolysis method, and the electrolysis rate is higher than the single-positive membrane and double-membrane three-compartment electrolysis. The electrodialysis method is used to treat nickel electroplating wastewater. The mass concentration of nickel ion in the cleaning water is ≥1.5 g/L to improve the dialysis rate. Electrodialysis concentration ratio is higher than reverse osmosis concentration ratio, which can be used to regenerate electroless nickel plating solution. Domestic experiments have proved that 90% of nickel sulfate can be recovered by electrodialysis, and the mass concentration of recovered nickel sulfate reaches 80~100 g/L, which can be directly used in the plating bath [24].
In conclusion, it can be seen that membrane separation technology has unique advantages in the treatment of nickel-containing electroplating wastewater. It can not only effectively remove Ni2+ from wastewater, but also discharge or reuse the wastewater at a low concentration. Moreover, the nickel-containing sediment trapped by the filter membrane can be recycled, which is both environmentally friendly and economical. Compared with other technologies, membrane technology has simple equipment, wide application range, high treatment rate and no need to add chemical reagents, so it will not cause secondary pollution [25]. However, membrane components are expensive and may cause membrane contamination during use, which is the problem that limits the wide application of membrane technology.
2.2.4 ion flotation technology
The method of ion flotation for nickel electroplating wastewater has high removal rate. Dai wencan et al. [26] found in their study on the treatment of electroplating wastewater by ion flotation that ion flotation has a very high removal rate of cadmium, zinc, copper, nickel and other metal ions, among which the minimum residual mass concentration of nickel is 0.33mg /L, and the nickel grade in foam products is 13.2%, which has a very high resource recovery value. Dong hongxing et al. [27] used flotation method to treat binary metal ion copper and nickel, and the removal rate of copper and nickel could reach 92.46% and 93.14% respectively. Tao yousheng et al. [28] used flotation method to conduct single treatment and mixed treatment experiments on nickel and copper ions, and the recovery rate of nickel ions in a single experiment could reach more than 99.5%. In the mixed experiment, the recovery of nickel ion and copper ion was significantly improved, and the recovery of copper ion reached 100%.
Ion flotation method has the advantages of extraction method and ion exchange method, and has the characteristics of wide range of application, high removal rate and recovery of valuable metals in electroplating wastewater. However, the application of ion flotation in the treatment of heavy metal wastewater is limited to the separation of single component, and there are few researches on the treatment of two-component and multi-component wastewater.
