Surface Modification Of Pyrophyllite For The Removal Of Hydroquinone From Aqueous Solutions

Natural pyrophyllite mineral belongs to the family of silicate minerals, which has drawn more and more concerns in recent years. It's not only because it has many advantageous properties, but also it is valued for its special advantages, such as: (1) vast reserves, cost effectiveness and easy acquirement; (2) activation or modification briefness; (3) removal of organic contaminants from waste waters; (4) higher stability. Aiming at the above-mentioned advantages as well as an economic view, for the moment, a number of studies have been performed using natural pyrophyllite or treated pyrophyllite as a novel and efficient adsorbent instead of activated carbons of the relatively high cost, and effort has been made to try to utilize this occurring adsorbent to remove toxic contaminants including heavy metal ions and organic pollutants from waste waters in wastewater treatment abroad. However, no reports on exploitation and utilization of pyrophyllite mineral as a sort of cheapness and novel environmental protecting material are found in China. Consequently, it is of great significance in theory and practice that researching on activating treatment of natural pyrophyllite mineral, in order to boost the active-sites at the surface of pyrophyllite mineral to replace the traditional wastewater disposal materials, and to achieve higher adsorption efficiency for organic pollutants.The aim of this study is, firstly, to use the natural sedimentation method and the suspended diffusion method to carry through purification of natural pyrophyllite mineral respectively, and to use the chemical whitening method to treat purified pyrophyllite samples; furthermore, to utilize different modifiers to modify natural pyrophyllite mineral according to the wet method; finally, to use hydroquinone solutions to interact with modifiers-treated and also untreated pyrophyllite powder. The removal efficiency of samples can be detected by quantitative analysis of infrared spectrum. In addition, this study also analyzes the effects of various factors on the modification, and optimizes the conditions of preparation craftwork, in order to improve the removal efficiency and adsorption capacity of natural pyrophyllite mineral; on the basis of experimental results, the main mechanisms of modification and adsorption have been primarily discussed,the following conclusions can be drawn from the experimental results.1. Mineral and chemical composition of seven pieces of pyrophyllite ore samples of Hei Long-jiang province are detected by analysis of X-fluorescence spectrum and infrared spectrum. It is considered that the components of pyrophyllite ore are quite complex and it has unequal purity. The result of whiteness testing indicates that the whiteness of samples with low purity is also lower.2. According to component feature, No.2 and No.3 are purified respectively, and the optimum conditions are determined by experiments. Solid to liquid ratio is 1:12; the purifying time is 1min in the primary process of purification. The purifying time is 5min, and adding concentration of dispering agent hexametaphosphate is different according to the variety of samples in the secondary process of purification. No.2 is 1.0%, and No. 3 is in need of 1.5%. Pyrophyllite of the purified sample of No.2 amounted 89% of the total contents by the natural sedimentation method and the suspended diffusion method, and the content of impurity can be observably decreased in great part.3. Purified pyrophyllite samples are treated with different reagents by the chemical whitening method, and the optimum conditions are determined by experiments. The concentration of hydrochloric acid or sulfuric acid is 30%; solid to liquid ratio is 1:10; whitening reaction temperature is 60℃~70℃; reaction time is 4h. Whitening handling can increase whiteness of samples from 27.26% to 71.83%, and ratio of eliminating iron of samples can achieve 94.02%.4. Various affecting factors on the adsorption capacity of hydroquinone molecules in solution by natural pyrophyllite mineral are optimized. The interaction between untreated pyrophyllite powder and hydroquinone solutions can be carried out according to the proportion of 1:8 and reaction time of 25min at room temperature. The granularity of natural pyrophyllite powder is less than 200mu, and PH value of hydroquinone solutions is 6.05-6.25. Preliminary experimental studies performed for the adsorption of hydroquinone molecules on natural pyrophyllite mineral reveal that hydroquinone molecules can be removed only 26.8% from aqueous solution.5. It is proved that the low adsorption capacity of natural pyrophyllite mineral can be enhanced by surface modification and that chemical modification of pyrophyllite would be useful for the preparation of new adsorbents for the economic treatment of hydroquinone molecules. Various affecting factors on the process conditions of activating treatment are optimized according to the adsorption capacity of hydroquinone molecules in solution by organo-pyrophyllite. The activating treatment can be carried out according to the dosage of 1%, reaction time of 2h and modification temperature of 75℃. The modifiers are respectively PAM and CTMAB.6. Various affecting factors on the adsorption capacity of hydroquinone molecules in solution by modifiers-treated pyrophyllite are optimized. The interaction between modifiers-treated pyrophyllite powder and hydroquinone solutions can be carried out according to the proportion of 1:8 and reaction time of 30min at room temperature. The granularity of organo-pyrophyllite powder is less than 200mu, and PH value of hydroquinone solutions is 6-7. Moreover, the removal efficiency of hydroquinone molecules in solution by modifiers-treated pyrophyllite is determined. That PAM-treated pyrophyllite powder is 83.1%; CTMAB-treated pyrophyllite powder is 79.3%.7. Based on infrared spectral analysis of modifiers-treated and untreated pyrophyllite powder, the author studies on the surface modification of pyrophyllite by polyacrylamide and quaternary ammonium salts of different length of carbon chain. It is discovered that interactions between modifiers and natural pyrophyllite are bonding function in the process of activation, not physical adsorption. The XRD analysis can also provide brief information that the structure was not changed since the original peak positions of pyrophyllite and were almost same. The XRD pattern of pyrophyllite is slightly affected by quantity of reagents, as observed by the change in the peaks corresponding to (001). The reaction between amine groups of polyacrylamide and hydroxyl or oxygen atom of the surface of natural pyrophyllite can form H-bonding, in order to achieve physical adsorption between natural pyrophyllite and polyacrylamide; when concentration of quaternary ammonium salt is more than cmc, cationic surfactant molecules are able to form micelle in aqueous solution,in order to achieve physical adsorption between natural pyrophyllite and quaternary ammonium salt. 8. The main mechanisms for natural pyrophyllite and modified pyrophyllite to sorb hydroquinone molecules in water system are also discussed. Batch adsorption experiments showed that polar hydroquinone molecules are adsorbed on negatively charged pyrophyllite surface through hydrogen bonding, and/or charge transfer complexes; the H-bonding interactions between dissociated phenolate ion and protonated amine groups on the polyacrylamide molecules attached to the surface of pyrophyllite drive the adsorption of polar hydroquinone molecules; the surface of quaternary ammonium salt-treated pyrophyllite powder can be conjugated to polar hydroquinone molecules, which mainly depend on hydrophobic surfaces of pyrophyllite and the interactions between dissociated phenolate ion and counter-ion contained the second adsorbent layer.