Combined Induced Crystallization Process For The Iron-containing Heavy Metal Wastewater Treatment

The threat to humanity by the heavy metal wastewater and the ecological environment is becoming more and more serious.In addition, the wastewater is a kind of composite resource with high-value utility.Therefore, it is consistent with the concept of sustainable development to explore the technology which can make the heavy metal wastewater harmless and resource. Although the traditional chemical precipitation can remove contaminants effectively, it may bring a large amount of difficult to handle and high operating cost of the chemical sludge. Moreover, it is difficult to achieve the resource utilization. When applying the crystallization method,it can cut the cost effective and improve the recovery and utilization value immensely.In the study, we carry out the research on the removal efficiency and the strategy of the heavy metal for the wastewater.Furthermore,we inspect the entire process continuous operation efficiency of the simulated wastewater and the recycling in the regenerating procedure by the combined process of "induced crystallization+sand filtration+ion exchange".The results show that the ferrous of the iron-containing heavy metal wastewater could be removed effectively by induced crystallization.The basic operating parameters of the crystallisation reactor are as follows: applying Na2CO3 as the precipitating agent, the particle size among 80 to 120 mesh as the induced carrier, the carrier filling ratio to be 0.67.The experiment shows that w hen the influent concentration of ferrous is about 100 mg/L, the crystallization removal rate can be exceed of 95%. The comprehensive optimum operating parameters are as follows: the influent p H adjusted to 3.0³.5, precipitant dosing ratio of 2.0: 1 or so, HRT=40 min, hydraulic loading reaching 31 m/h, corresponding to the reflux ratio achieving（14¹5）: 1. We conduct that the chemical formula of the crystalline product is Fe O（OH）·Fe CO3 according to SEMEDX and XRD.Moreover, the ferric ion is difficult to be effectively removed by induced crystallization and it may affect the crystallization process of other ions.The study of the crystallising treatment strategies of the wastewater containing iron and complex showes that when dosing H2O2 to broken the complex, then using sulfites to reduce the Fe³⁺, it can be effectively removed by crystal after these pre-treament.The testing influent is the simulated electroplating wastewater containing 150 mg/LFe2+, 100 mg/LCu2+, 100 mg/LEDTA and 100 mg/LCOD. When the initial p H is about 3.0, the dosage of H2O2 about 0.46 g/L, the reducing agent dosage about 1 to 1.25 times of the equivalents, the reaction about 30 min, the complex broken rate and the reduction rate can be up to 90% and 80%.And the TOC concentration of the effluent can decrease to 45 mg/L or less after treating. Also the crystallization removal efficiency can increase by 60% compared with non-pretreated.When applying the combined process to treat the simulated wastewater, the continuous operation shows that the entire process can be recovered efficient of heavy metals. When the average influent contains Ni2+ 100 mg/L, Cu2+ 65 mg/L, Fe2+ 200 mg/L, Fe³⁺ 50 mg/L, COD100 mg/L, EDTA100 mg/L, dosing H2O2 to break complex and reducing sequentially, all the indicators can meet the national emmision standard during the 8 days continuous operation. The regenerated liquid of all process units can be recycled and the recovery rate of nickel, copper, iron can be up to 99.8%,99.6%,97.8% respectively.