A Study On Coagulant-adsorption Process Treatment Of Wastewater From Printed Circuit Boards Wet Process

In order to reuse of wastewater which produced by the wet process of disposing wastedprinted circuit boards, adopt coagulant-adsorption process. Polyaluminum chloride （PAC） andpolyferric sulphate （PFS） are used as coagulant. Study on the effects of the removal ofturbidity and CODcrconsidering the factors of detention time,pH,G value,coagulants dosageand aid coagulant on coagulation.The results show that exceed99%and80%of tuirbidity andCODcrcan be repectively removal when coagulant dose of PAC and PFS is75mg/L and150mg/L under pH between7.0and8.5; exceed98%and90%of turbidity and CODcrcan berespectively removed while reaction stirring velocity is in the range of50¹00r/min,correspond G value is of8.77²2.41s^-1,and dosing aid coagulant,PAM,can reduce the PACor PFS dosage and accelerate setting velocity.The optimal opration conditions by orthogonalexperiment are10mg/L PAC,0.5mg/L PAM,and stirring velocity of50r/min and G value of8.77s^-1,and99.39%of turbidity and88%of CODcrcan be removed respectively;the effluentcan meet the requirement of reuse standard with turbidity of1.1NTU,CODcrof41.74mg/L,SS of5mg/L respectively.Coal fly ash carbon which has higher carbon content is acquired through flotationexperiment. It is beneficial to adsorb Cr（Ⅵ） at pH=2,The time of the adsorption equilibrium is120min. Aqueous solutions are in good agreement with the pseudo-second rate equation.The correlation coefficient of adsorption isotherm of coal fly ash carbon Langmuirthermoisopleth is obviously higher than Freundlich and Temkin thermoisopleth. The range ofcorrelation coefficient of activitied carbon is Freundlich>Temkin> Langmuirthermoisopleth.The adsorption capacity of coal fly ash carbon and activitied carbon is4.67mg/g and11.31mg/g respectively.Coal fly ash carbon absorbs Cr（Ⅵ） is an endothermic process,while activied carbonabsorbes Cr（Ⅵ） is exothermic process. After the addition of competing anions Fe（Ⅲ）, Coalfly ash carbon and activitied carbon still obey Langmuir for adsorbing Cr（Ⅵ） and Fe（Ⅲ）. Themaximum saturated adsorption capacity of Cr（Ⅵ） and Fe（Ⅲ） are decreasing.Alkalic desorption is much better than acidic desorption for adsorbent.The optimumconcentration of alkalic desorption for coal fly ash carbon and activitied carbon is0.05mol/L and0.2mol/L.After coagulation, adding5g/L coal fly ash carbon into wastewater which produced bythe wet process of handing the wasted printed circuit boards,shaking120min at25℃ temperature without adjust pH.Cr（Ⅵ） concentration can be removed91.94%, the wastewater cansteadily meet the requirement of the drail standard.The functional groups present on activited carbon included—OH,C=C,C=O andC—O,which main factors for Cr（Ⅵ） sorption,while The functional groups present on coal flyash carbon included—OH,C—O and ionic adsorption.coal fly ash carbon and activitied carbon have been found dichromate which adsorb onadsorbant surface and reacted oxidize and deoxidize,change Cr（Ⅵ） to Cr（Ⅲ）。...