| Not only the outlet of wastewater containing heavy metals wastes lots of resourses,but also influences the safety of drinking water.So the treatment of the wastewater has always been an important project in the world environmental protection.At present,various conventional treatment methods such as lime-neutralization-precipitation,ion exchange and active carbon adsorption have a lot of shortages such as difficult to realize deeply purified or high cost.In addition,the yearly output of spent grains(SGs) is more than ten million tons in China.Most of it was deposited for disposition to lead to severity pollution.So it is of important to develop the study related to deeply purifying water containing heavy metals and the comprehensive utilization of SGs in order to protect our environment.Based on the characteristics of biosorption being a rapid,reversible, economical and ecofriendly technology and that of SGs large quantity and easy gained,deeply purified water containing arsenic and cadmium using spent grains as biosorbent technique has been put forward.Also the technique is to conform the new (GB5749-2005),brought into effect in our country at 1/7/2007,in which the concentration of arsenic has fallen from 0.05 to 0.01 mg/L,and that of cadmium is 0.005 mg/L.In the dissertation SGs was chosen as raw material for adsorbent,arsenic(Ⅲ,Ⅴ) being a representational anion and cadmium a representational cation in industrial wastewater as treating object.The treatment technics parameters and purified mechanism of SGs biosorbent for arsenic and cadmium were systemic investigated.The technical bottleneck that only under the condition of oxidating As(Ⅲ) to As(Ⅴ) can the purified water treated by traditional technology has been broken through.The objective that water containing arsenic and cadmium being high efficient purified has been achieved.The biosorption behavior of As(Ⅲ),As(Ⅴ) and Cd(Ⅱ) from water by SGs has been analyzed.The modifier Ca(OH)2 for SGs to deeply purified arsenic and cadmium has been chosen,which can increase the purified efficiency for arsenic and cadmium ions by a long way.The adsorptional efficiency for As(Ⅲ),As(Ⅴ) and Cd(Ⅱ) from water by SGs can be enhanced 83.4,37.4,14.6%respectively by adding Ca(OH)2 to SGs than that of NaOH.Only the dosage of SGs which granularity less than 0.833 mm 1 g/L after modified to be biosorbent can get to the maximum efficiency for arsenic and cadmium.The particle size of biosorption has little effect on the purifying process.The sorption of As(Ⅲ) and As(Ⅴ) increased with increase in contacting temperature at 283 K—313 K,but sorption of Cd(Ⅱ) go against with it.The simulated analysis indicated that Langmuir isotherm was well fit to the experimental data of sorption of As(Ⅲ),As(Ⅴ) and Cd(Ⅱ) by SGs.At 303 K the maximum sorptional capacity of As(Ⅲ),As(Ⅴ) and Cd(Ⅱ) were 2.125,3.089,2.166 mg/g,respectively.Through various testing means such asξ-potential,Fourier transform infrared absorption spectrum,energy spectrum and X-ray diffraction,the biosorptional mechanism of biosorption of arsenic and cadmium ions by SGs biosorbent to has been put forward.The characteristic of cellulose and lignin were the mainly function groups at the surface of SGs.The biosorption of arsenic and cadmium ions occurred mainly at the cell wall of biosorbent.And static sorption between SGs and As(Ⅲ),As(Ⅴ) and Cd(Ⅱ) were mainly biosorptional mechanism,which the optimal pH were 11.5～13.0,11.5～13.0,8.0～11.5,respectively.The high efficient for purifying arsenic and cadmium ions by biosorbent,not only for the modifier interacting with As(Ⅲ),As(Ⅴ) to make Ca5(AsO4)3(OH) and Ca5(AsO3)3(OH)·4H2O,respectively,and with Cd(Ⅱ) to gain Cd(OH)2,but the carboxyl and hydroxyl groups at the surface of SGs were interacted with arsenic and cadmium ions.The hydroxyl in carboxylic acid was replaced by arsenite or arsenate to yield carboxylic acid ramification,and hydrogen H in carboxylic acid to obtain carboxylic acid cadmium.The kinetics mathematical model of sorption column packing SGs biosorbent was established,and the breakthrough curve under different conditions was calculated.Using various kinetics equations the sorption kinetics process of arsenic and cadmium by SGs biosorbent was discussed.The study indicated that the sorption for As(Ⅲ),As(Ⅴ) and Cd(Ⅱ) by SGs was a rapid first and slow later process,which according with pseudo second-order kinetics equation.The curve qt to t0.5 of sorption being a line not through initial point at 50～90 min illuminated the interior diffusion was not the only rate-limiting step at purifying process for arsenic and cadmium by SGs,but united-controled by film diffusion and granule interior diffusion.Compare with the rate of extenal diffusion,that of granule interior diffusion was a key deciding the whole sorption process.At dynamic process,the figure of breakthrough curve was related to experimental conditions,such as flow rate of solution, initial concentration of sorbate and the column height.The calculated result through kinetics mathematical model was coincidence with the experimental result,which to some degree validated the reliability and correctness of model.Aimed at the fact that other ions being in the actual industrial wastewater,the effect of various anions and cations in the system on sorption of arsenic and cadmium by SGs was studied.At the same time, the behavior of arsenic and cadmium coexist was also analyzed.The strippant was chosen,and desorption temperature that affect the desorption process on arsenic and cadmium from SGs were investigated. Meanwhile,the regeneration utilization behavior of biosorbent was researched.Moreover the continuum-experimental study on deeply purified the outlet wastewater from one metallurgical plant at Hunan by SGs biosorbent was fulfilled.The results indicated that at inlet velocity of flow 1.36 mL/min,the time of break-through were 400 min and 320 min for arsenic and cadmium,respectively when using SGs to continuously purify the wastewater containing 2.860 mg/L of arsenic and 9.957mg/L of cadmium.After two rounds of sorption-regeneration the times of break-through were 160 min and 150 min for arsenic and cadmium, respectively adsorpted by biosorbent,which indicated that the SGs biosorbent has highly purified effect for metallurgical wastewater.
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