(School of Resources and Environmental Engineering, Wuhan University of Technology, Wuhan, Hubei 430070)
First, the content introduction
1) experimental results show that the amount of intercalation agent affects the interlayer spacing of montmorillonite organic intercalation compounds. The optimum dosage of intercalation agent for preparing montmorillonite organic intercalation compound is 120%CEC, and the interlayer spacing of calcium-based montmorillonite organic intercalation compound (GY) is increased from 1.556nm of calcium-based montmorillonite (original soil) to 65436 nm. The interlayer spacing of organic intercalation compound (NY) in sodium-based montmorillonite increased from 65438±0.296nm to 2.045nm. The adsorption effect of organic modified montmorillonite on Cr (ⅵ) was obviously higher than that of undisturbed soil and sodium-modified soil, and its adsorption removal rate increased with the increase of the amount of intercalation agent added during modification. When it exceeds 100%CEC, the adsorption removal rate of low concentration Cr (ⅵ) wastewater does not increase with the increase of the amount of intercalation agent. The adsorption removal rate is affected by pH value, reaction time, adsorbent dosage and initial concentration of wastewater. The optimum pH value of montmorillonite organic intercalation complex adsorption is 3, and the adsorption equilibrium time is 60 min. The adsorption removal rate increases with the increase of adsorbent dosage and decreases with the increase of initial concentration. Under the optimum experimental conditions, namely pH 3, adsorption reaction time 60 min, adsorbent dosage 2 g/ 100 mL, the adsorption removal rate of wastewater containing Cr (ⅵ) reached 98%, and the residual concentration of wastewater after treatment was lower than the national discharge standard. The results show that Cr (ⅵ) mainly exists in water in the form of anionic groups such as, etc., and it is difficult to enter the montmorillonite layer, so the adsorption effect of undisturbed soil and sodiumized soil is not good. Cetyltrimethyl ammonium bromide intercalation agent not only enters the interlayer through cation exchange, but also is attracted into the interlayer through hydrophobic bond, and the insertion amount exceeds 100%CEC, which significantly improves the interlayer spacing and adsorption effect, so it can effectively remove Cr (ⅵ) ions from wastewater.
2) Using inorganic-organic pillaring technology, taking natural calcium-based rectorite from Zhongxiang, Hubei Province as raw material, after mineral processing, purification and sodium modification, TiCl4 _ 4 was used to prepare pillaring agent, and then sodium-based rectorite was pillared with this pillaring agent and cetyltrimethylammonium bromide under different conditions. The colloid value, swelling property and swelling value of rectorite after sodium modification are 7.5 ~ 16 times higher than those before sodium modification, 5 ~ 25 times higher than those before sodium modification. Rheological properties and dry-wet compressive strength were significantly improved. The preparation of pillaring agent usually uses Keggin ion of hydroxyl aluminum prepared by alkaline hydrolysis of AlCl3 as pillaring agent. The diameter of hydroxyl titanium ion used as pillaring agent is larger than that of hydroxyl aluminum ion, which can obtain larger interlayer spacing, but its preparation is complicated and difficult to control. Especially TiCl4 _ 4 _ 4 is easy to hydrolyze in air, and the reaction in nitrogen environment solves this problem. On the basis of pillared rectorite formed by inorganic pillaring, further inorganic-organic pillaring with cetyltrimethyl ammonium bromide can effectively expand the interlayer spacing of bentonite and obviously improve its thermal stability, thus obtaining better pillared products. The adsorption treatment conditions of inorganic-organic pillared rectorite for wastewater containing Cr (ⅵ) were optimized by orthogonal experiment, and the adsorption treatment process conditions were determined, and the adsorption removal rate reached 98.0%. The experimental study shows that the adsorption and removal effect of inorganic-organic pillared rectorite on wastewater containing Cr (ⅵ) is obviously higher than that of original soil and sodium soil, and it is a new clay mineral functional material with excellent performance.
3) The simulated wastewater containing chromium and the actual wastewater from Daye Nonferrous Metals Company were treated with goethite, and the best adsorption treatment conditions were obtained. The highest adsorption removal rate of chromium ions was 98.26%. The secondary adsorption experiment was carried out with goethite adsorbed with chromium ions, and the removal rate reached about 80%, indicating that goethite can be reused. The desorption experiment in fresh water medium (the initial concentration of the sample is 20mg/L under the same conditions as the adsorption experiment) shows that the desorption rate of Cr3 ++ is 0.3 18%, which is 9.64%, indicating that goethite has a strong fixation ability for heavy metal ions.
At present, the main problem that restricts the application of mineral materials in the treatment of wastewater containing heavy metals is the desorption, regeneration and recovery of heavy metal ions after adsorption of mineral materials. Mineral materials adsorbed with heavy metal ions, if not regenerated, will form solid waste, occupy land and cause secondary pollution. At present, the regeneration of mineral materials at home and abroad mainly adopts chemical reagents such as acid, alkali and salt or methods such as high heat, magnetic field and microwave. These methods either have poor regeneration effect or change the mineral structure, so that mineral materials can not be reused many times. In this project, the liquid membrane emulsion extraction technology is used to desorb and regenerate the mineral materials after absorbing heavy metal ions, so that heavy metal ions can be recovered and secondary pollution can be avoided. This technology has achieved good results through repeated tests on a variety of heavy metal ions (Cu2++, Pb2++, Cr3 ++ and Ni2++) and mineral materials (rectorite, bentonite and zeolite), and applied for a national invention patent (liquid membrane emulsification technology for recovering heavy metal ions at the interface of mineral materials).
Second, popularization and application
The results of this project are innovative, which provides an efficient and cheap clay mineral water treatment agent for effectively removing heavy metal ions from wastewater, and also opens up a new application field for China's rich and cheap clay mineral raw materials, which has theoretical significance and application prospects.
For example, organic intercalation compounds of montmorillonite, inorganic-organic pillared rectorite, goethite and other water treatment functional materials, the adsorption removal rate of chromium-containing wastewater reached 98%, and the residual concentration after treatment was lower than the national discharge standard (0.5 mg/L). The actual wastewater containing heavy metals in the smelter of Daye Nonferrous Metals Company has also been successfully treated.