| Chrome-tanning method was irreplaceable and widely used in leathertanning industry due to plays an excellent effect on the finished leather. However,the combination amounts of trivalent chromium during traditional chrometanning process is not very high, and the microorganisms have no ability todecompose the left chromium in the waste water so that these chromiums have tobe discharged into the environment along with the waste water, and what’s worse,they would pose a great harm to the people and the environment. In recent years,for the sake of chromium resource consumption and avoid exceedings of Cr(VI)into the environment, domestic and international experts investigated no-chrometanning technology in order to replace part of the chrome tanning, includingno-chrome metals (zirconium, aluminum, titanium) tanning methods. However,no matter domestic or overseas the study on using Zr, Al, Ti compositeadsorbents for removing chromium from chrome-tanning waste water is notmature enough. In such situation, A12O3-TiO2, ZrO2-TiO2, ZrO2-Al2O3andZrO2-Al2O3-TiO2composite oxides were firstly prepared by co-precipitation inthis work, and these oxides’ feasibility to remove EDTA-Cr from staticsimulation chrome-tanning waste water was studied as well. Secondly, the actualnon-chrome tanning waste water was filtered, dried and then made to be powder,which was used for adsorbing EDTA-Cr of simulation chrome-tanning wastewater. Futhermore, through studying above absorbents so as to achieve thechromium standards even no emissions, afterwards, realize the cleanerproduction mode of "waste reuse and recycle". Finally, for overall consideration,combining static and dynamic experimentsto study the feasibility of A12O3-TiO2and Al(OH)3for removal of chromium in the practical three-phase separatorfluidized bed reactor. The results were shown as follows:(1) The composite oxide adsorbents for the adsorption of EDTA-Cr were monolayer adsorbents. In the process of adsorbing EDTA-Cr, the specific surfacearea and pore volume had a significant influence on the adsorption properties.The absorbents with higher Al contents would have a bigger specific surface areaand with more absorption capacity when compared with other preaparedabsorbent. The adsorption capacity of composite oxide sorbents for EDTA-Crwas increased with the increasing of initial chromium concentration. In theexperimental range chromium concentration, the maximum adsorption capacitycan reach to138mg/g.(2)In the experimental range chromium concentration, The adsorptionequilibrium data of the EDTA-Cr and Cr(III) on ZrCF were9.7mg/g and12mg/g,respectively. The adsorption equilibrium data of the Cr(III) on sintered ZrCF was10.3mg/g. The removal rate of Cr(III) on ZrCF and sintered ZrCF were75%and50%.(3)The adsorption behavior of EDTA-Cr of precipitate adsorbentspreparated from the actual non-chrome tanning wastewater could be well fittedby Langmuir equation, and they were imporved to be monolayer adsorption. Theadsorption capacity of actual precipitates sorbents for EDTA-Cr was increasedwith the increasing of initial chromium concentration. The sample from tanningwaste water produced precipitates relative to the main sediment adsorbents had agreater advantage in the adsorption capacity; the maximum adsorption capacitycould reach to109mg/g.(4)Al(OH)3andAl-Ti was choosed because of theirs relatively highadsorption capacity from hydroxide adsorbentswhich prepared in the early timeof the subject study and the other adsorbens.And then, In laboratory, there was adynamic adsorption test for Al(OH)3andAl-Ti to adsorb the EDTA-Cr and Cr(III)ions by using the three-phase separator fluid bed reactor.Firstly, the mechanical properties of the water of the three-phase separatorfluid bed reactor, when the flow rate was4.8L/h, aeration was3.4L/min, and theaverage residence time was57.7min, the average residence time was mostclosest to the the oretical time(57.5min).Then, in the condition of certain flow rate and aeration, dose the watersample and adsorbents into the fluid bed reactor. In actual operation of thereactor, adding10g Al (OH)3to adsorb EDTA-Cr, it was still difficult to meet the state standards for waste water treatment, while its adsorption capacity for thetrivalent chromium ion [Cr(III)]was very good. We can obtain the results fromthe data, after seven hours of continuous reaction, the effluent in the reactor wasnot only meet the national standards but also improved the adsorption capacitywas still very good.In conclusion, the wastemade from no-chrome tanning wasterwater couldbe reused and be used as absorbents to treatment chromium in chrome-tanningwastewater. For the current treatment of non-precipitated chromium, it providesa valuable reference and enrichs the theory of removing heavy metal in tanningwaste water, and provides theoretical and technical basis for achieve to themulti-metal-tanning waste water reffluent standards. |
PDF Full Text Request