Study On Deactivating Heavy Metals In Sludge By Modified Fly Ash And Application

Firstly, this paper adopts orthogonal experimental method to prepare the modified fly ash ,and then optimizes the conditions of modification of fly ash after analyzing the influence factors of heavy metal deactivation in sluge by using the passivation and pillar eluviation experiments, all the above is established on the basis of analyzing the physicochemical properties of approval sludge and fly ash ; The effect of modified fly ash on state of Zn, Cu and Mn was studied. Besides, the properity comparison of heavy metal between deactivated sluge by modified fly ash and deactivated sluge by orginal sludge and deactivation mechanism were explored. Through pillar eluviation experiments and roof greening experiments of sedium lineare, the effects of modified fly ash with different mixture ratio and dosage treating sluge on environment were explored and the applicable feasibility was studied. Main study conclusions are as following:The contens of organic matters,total nitrogen and total phosphorus of approval municipal sludge are far more than those of the soil, but sludge also contains higher heavy metals and goes beyond agricultural use standard in our country such as Zn,Cu,Mn, especially Zn and Cu, 3300.0 mg.kg-1 and 920 mg.kg-1respectively. Therefore, the sludge is a very good fertilizer source and has higher value in use from point of view of the nutrients such as organic matter,nitrogen,phosphorus of the sludge. The sludge is confined in use because of outrageous heavy metal, so the sludge must be proceeded preliminary treatment before using.The approval municipal sludge contains relatively high level of SiO2 and Al2O3, and 50.3%and 23.20% respectively, which provides a good basis for its modification. Adopting orthogonal experimental method to prepare the modified fly ash.After passivation and pillar eluviation experiments, the influence factors of sludge heavy metals deactivation are analyzed by range analysis and variance analysis,. The results of experiments show that: calcining heat and mixture ratio should be controlled strictly when fly ash is modified. Considering influence factors comprehensively, The lime modification fly ash to passivate sludge heavy metals gets the best results while calcining heat (1000℃), mixture ratio(10%), calcining time (3h).With the mixture ratio increase of modified fly ash ,the contents of exchange state and organic incorporated state of Zn,Cu,Mn in the treated sludge have downtrend obviously, but the concents of ferrimanganic oxidation state and residual form of these have tendency to augment. The contents of the ferrimanganic oxidation state and residual form of heavy metal in sludge have reached high-level, while exchange state has reached low-level, when the mixture ratio of modified fly ash is 20%. Biological effectiveness and environmental effectiveness of heavy metal in sludge is reduced in consequence.Comparing the effienciency of deactivating sluge of modified fly ash and original fly ash in deactivating heavy metals of sluge, the effect of modified fly ash is obviously superior to that of original fly ash. Moreover, the effect can be explanated by the microscopic structure of modified fly ash. At first, specific surface area of modified fly ash is 2.5 times bigger than that of fly ash, so modified fly ash has better physical adsorption capacity and makes its' chemistry adsorption capacity increase meanwhile. Furthermore, aluminium silicate and silicate which are generated from modified fly ash have very strong ion exchange capability and can arise ion exchange with heavy metal in sludge, moreover, this process is non-eversible. Simultaneously, strong alkalescence and iron oxide of modified fly ash are all favorable to the precipitation of heavy metal in sludge.When modified fly ash was used to treat sluge and then was applied itn greening of sedum lineare, considering sedum lineare growing situation, leakage water affecting on quality of ground water, and reducing the cost of treatment when modifing fly ash ect., surrounding environment will not be polluted when sludge treated by 10%~20% modified fly ash is applied to sedum lineare roof greening, roof greening base material ----- red soil 3cm, upper treated sludge 5cm.