| AICI3·6H2O, MgCI2·6H2O and NH3·H2O being raw materials, a colloid particles sorbent - nano magnesium aluminium hydroxide MAH -was prepared by coprecipitation method. The MAH was studied by all kinds of chemical analysis methods and the modem techniques. The structure and morphology of MAH were studied by transmission electron microscope (TEM), X-ray diffraction (XRD), infra-red spectroscopy measurements; the electrokinetic property of MAH was measured by Zeta potential measurement. Tests about the application of MAH on dyeing wastewater treatment were made ; The effect factors were studied and the disposal mechanism was discussed. The experimental results showed that:(1) The optimum conditions for preparing colloid particles sorbent of MAH (magnesium aluminium hydroxide) were molar ratio of Mg/AI =3:1, temperature of peptizing kept at 80℃ for 3~4h. The MAH sample prepared is hexagonal multilayer in structure, which is similar with the structure of hydrotalcite crystal. The diameter of particles is 30~50nm. The MAH sample prepared contains a lot of -OH on the surface. The MAH particles had perpetual positive charge. Zita potential is positive in lower pH ambient, and decreases with increasing pH. When pH exceeds the isoelectric point (IEP), Zita potential appears negative. The isoelectric point of MAH was pH=10.9.(2) Effects of the molar ratio of Mg / Al in mixed solution were studied. The molar ratio of Mg / Al in mixed solution 3:1 was the most effective at removing dyes. The MAH sample prepared was effective for the removal of various dyes. MAH sorbent exhibits the potential to be applied in water purification.(3) Effects of time, pH, dose, the concentration of dyes, temperature were studied. MAH sorbent has the speciality that it is available in the treatment of effluent streams from diverse wastewater processes. The decoloring effect of MAH on anionic dye wastewater mainly resulted from chemical absorption, and absorption performance followed Langmuir formula very well. There wereno apparent differences when the pH range was 4-11, within which adsorption process could finish in 20min. High temperature is unfavourable for adsorption process.(4) The spent MAH sorbent can be regenerated easily by heating at 450°C for 5h to remove all adsorbed dyes. MAH sorbent loses its structure during calcination at 450°C. However, the structure is restored when the calcined sample is dispersed into an aqueous solution. This allows the sorbent to again adsorb dyes from wastewater. In fact the calcined MAH (CMAH) demonstrated better ability to remove dyes. Hence, MAH sorbent is easily recoverable and reusable so that it is a promising sorbent.(5) In practical treatment, the decoloring rate and COD removal of MAH were higher than that of PAC or PFS. But it is lower than the single dye wastewater because of different kinds of assistants contained in the practical wastewater.(6) It is proven that dyes were adsorbed by MAH through the infra-red spectroscopy measurements. The two possible mechanisms involved in the adsorption process are physical adsorption and chemical adsorption. Firstly, dyes may be adsorbed on the ionic MAH's surface. The parameter of sorbent surface area plays a key role in this mechanism. The second adsorption mechanism involves anion exchanges. MAH demonstrated a propensity to remove anionic dyes. It is apparent that the second adsorption mechanism prevails and accounts for better uptake levels.(7) The MAH sample prepared has three specialties as a sorbent: (fbbvious removal of dyes attained at low dose with high adsorption rate.?solid and liquid dividing easily and no secondary pollution produced, ?convenient and fast to operate, no need for complex equipment. |
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