Preparation Of Decolorizing Ceramsite For Printing And Dyeing Wastewater With Acid And Base Treated Clay And Its Mechanism

Printing and dyeing wastewater is a considerable source of environmental contamination, and its decolorization is the main problem. In recent years, the preparation of decolorizing materials for printing and dyeing wastewater with clay minerals as principal raw materials, such as palygorskite, bentonite, sepiolite and so on, have been widely studied.According to the decolorization mechanism, the preparation methods of decolorizing materials are mainly divided into two types: washed thoroughly with distilled water followed by high-temperature acid activation, the active floridin made by this way is mainly with physical adsorption; soaked in metal-salts solution or added metal-salts as additives directly, the decolorization mechanism of the material made by this way is chemical flocculation reaction of metal ions. Each has its merits, but the problems restricting the application of the materials still exist: such as the large quantities of acid water created during the process of acid activation, the separation of mushy stage existing in the process when powdered materials were used, the low strength granular material, non- or low-reusability.In this work, the decolorizing ceramsite for printing and dyeing wastewater was prepared by means of acid activation at normal temperature(20～25℃), base neutralization, granulation and heat treatment, by using clay minerals, such as palygorskite, as raw materials. Based on the quantitative decolorizing investigation of the three-colour wastewater containing single reactive, dispersive, and vat dye, the manufacturing technology of decolorizing ceramsite was optimized, the mechanism of preparation and decolorization was discussed, and the strength, loss ratio and reusable method of the decolorizing ceramsite were studied. In addition, the performance of the decolorizing ceramsites prepared with palygorskite, bentonite, sepiolite and Hangjin2# clay was compared. The main conclusions are as follows:1. The optimum manufacturing technology of decolorizing ceramsite is that, acid activation for 1.5 h at normal temperature, the ratio of clay mineral (<0.180 mm) to H₂SO₄(2.5 mol/L) was 1 to 2.5, alkali neutralization (NaOH, 5 mol/L) to pH value about 7-8, one time filtration, granulation (3-5 mm), oven drying at 90℃for 2 h, heat treatment at 700℃for 1 h.2. The performance comparison of the materials made of different clay minerals shows that, the dcolorizing ceramsite made of palygorskite or Hangjin2# clay has best performance. With a decolorizing ceramsite dosage of 2 g/L after 5 min static treatment at normal temperature, the decolorization ratio of wastewater, with the initial pH value of 9-12, containing single pure dye of different properties, is more than 90%. After 5 min static treatment to actual printing and dying wastewater at normal temperature, the dcolorizing ceramsite made of palygorskite has a decolorizing amount of 635 mL/g and the reduction in COD of 81%, while the dcolorizing ceramsite made of Hangjin2# clay has a decolorizing amount of 565 mL/g and the reduction in COD of 73%.3. The dcolorizing ceramsite made of palygorskite or Hangjin2# clay is of high strength. Oscillated for 30 min, its loss ratio is less than 5%. Soaked in water for 20 days, the dcolorizing ceramsite can not be disruptive. The using of such ceramsite can avoid the disadvantage of low dcolorizing velocity by using traditional physical method. The dcolorizing velocity of such ceramsite is as fast as powdered material.4. Base neutralization followed by acid activation is the key step, which results in the dcolorizing ceramsite with excellent chemical flocculation. The property of high strength is originated from the calcination at high temperature. The decolorization effect of the prepared material is mainly attributed to the combined chemical flocculation reaction of various metal ions of the material, plus little physical adsorption.5. Treated with saturated (NH₄)₂SO₄ solution for 10 min, and calcined at 300℃for 10 min, the used decolorizing ceramsite can be reused, with reuse time up to 15.6. The separation of mushy stage existing in the process when powdered materials are used can be solved effectively by using the decolorizing ceramsite treatment. This makes it possible for the reuse of the material, and can avoid the material from the secondary water pollutant. The ultimate treatment pH of about 7.5 makes it pollution-free for the discharging wastewater.