| Hydroxamic acids are new kinds of flotation reagents with the characteristic of toxicity and are broadly applied in mineral flotation. At present, the studies on biodegradability of such compounds are really rare. So the evaluation of biodegradability of hydroxamic acids will provide a certain theory for the treatment of waste water.Four kinds of hydroxamic acid collectors benzohydroxamic acid, salicylic hydroxamic acid, N-hydroxy phthalimide and H205(2-hydroxy-3-naphthalene A hydroxamic acid) were selected as objects of the study. The biodegradability of hydroxamic acid collectors had been evaluated by BODs/CODcr, oscillating culture method, permanganate index method and modified Sturm method. Besides, the biodegradation kinetics models have been studied. The biodegradation characteristics of the four kinds of hydroxamic acids in a sole substrate and with added carbon source and nitrogen source for co-substrates conditions were compared. The quantitative structure-biodegradability relationship (QSBR) model of hydroxamic acid mineral flotation collectors was established. Finally, the biodegradation mechanism of hydroxamic acids was preliminarily discussed. The following main conclusions were obtained by the above experiments.(1) In the experiments of BOD5/CODCr ratio method, the BOD5/CODCr ratios of benzohydroxamic acid, salicylic hydroxamic acid, N-hydroxy phthalimide were respectively0.35,0.33,0.32, The ratios were all more than0.3, so the three kinds of compounds were classified as biodegradable organics. H205with the BOD5/CODCr ratios of0.09could be classified as hardly biodegradable organic.It could be known that by the experiments of oscillating culture method, benzohydroxamic acid, salicylic hydroxamic acid, N-hydroxy phthalimide were biodegraded rapidly, but H205was biodegraded slowly. The biodegradation of the four compounds followed the first order kinetic equation and the biodegradation kinetics equations were as follows, C=29.32e-0.17717t,C=30.38e-0.6415t,C=29.61e-0.5413t and C=29.85e-0.1012t.The biodegradation rates by permanganate index method of benzohydroxamic acid, salicylic hydroxamic acid, N-hydroxy phthalimide, H205in8d were respectively 58.78%,54.37%,50.36%,18.26%. And the biodegradation rates in20d could reach83.35%,80.88%,79.68%,27.52%. The first three compounds were classified into biodegradable organics. H205was hardly biodegradable organic. The degradation rate of sodium oleat was100%, suggesting that the experiment was valid.The Modified Sturm Tests indicated benzohydroxamic acid, salicylic hydroxamic acid,N-hydroxy phthalimide and H205in28d were respectively75.09%,72.97%,70.21%,-22.62%. And the values of ultimate IB were199.37,189.46,187.40,72.06. so the first three kinds of compounds were biodegradable organics. H205was hardly biodegradable organic.It could be obtained by the above four kinds of methods that benzohydroxamic acid, salicylic hydroxamic acid, N-hydroxy phthalimide were easily biodegraded and belonged to easily degradable organic compounds, while H205was difficult to biodegrade and belonged to refractory degradable organic compound.(2) The four kinds of hydroxamic acid collectors hadn't good biodegradability in the sole substrate condition. The biodegradation process of the four compounds all followed the first order kinetic equation. The microorganisms in activated sludge hadn't reached saturation by the substrate, the biodegradation rates of hydroxamic acids increased with the increasing of the initial concentrations.Effects of different concentration of carbon sources and glucose as co-substrate on biodegradation of hydroxamic acids were investigated. The degradation rates of benzohydroxamic acid, salicylic hydroxamic acid, N-hydroxy-phthalimide and H205with the presence of additional carbon source glucose and nitrogen source peptone were increased from68.2%,78.3%,56.5%,36.84%in the sole substrate condition to99.26%,99.03%,98.17%,53.87%respectively. So a conclusion could be made that cometabolism was an effective way to enhance the biodegradability of hydroxamic acids.(3) The (QSBR)pri model of hydroxamic acid collectors was established for primary biodegradability prediction as k=2.4083+0.1471EHOMO-0.4703C loggP (R2=0.9530). The (QSBR)ult model for the ultimate biodegradability prediction was obtained similarly as PCD=0.9704-0.0757EHOMO-0.9628CLogP,(R2=0.9022), The biodegradability of hydroxamic acid collectors was affected by EHOMO,ClogP significantly. During the UV and infrared spectroscopic analysis, the biodegradation pathway of hydroxamic acid was discussed. It could be preliminarily considered that the benzene ring structure of hydroxamic acid was degraded to phenol and then catechol firstly. The catechol was oxidized to carboxylic acid and aldehyde which were further oxidized to hexadiene diacid and2-hydroxy-hexadiene acid. The final products were CO2and H2O.The main innovations and the significance of the thesis were as follows:(1) The biodegradability of the hydroximic acid collectors were studied completely and systematically with four different kinds of evaluation methods which complemented each other to avoid the limitations of the single method which provided scientific basis for the treatment of hydroximic acid wastewater.(2) The biodegradability of the hydroximic acid collectors was studied under the single substrate conditions and under co-substrate conditions. It showed that the presence of carbon source, nitrogen source could shorten the reaction time and improve the degradation rates, especially better for refractory organics H205. It was found that cometabolism was an effective way to improve the biodegradability of the hydroxamic acids which provided a new means for the treatment of ore dressing wastewater.(3) The (QSBR)Pri model for primary biodegradability prediction and the (QSBR)ult model for ultimate biodegradability prediction of hydroxamic acids were obtained. The determinants of the hydroxamic acids biodegradation were discussed with the QSBR models which provided a basis for the prediction of the biodegradability of hydroxamic acids and for the design and synthesis of new environment-friendly hydroxamic acid collectors. |
