| HPF coking desulfurization Waste Solution(DWS)is a serious contaminants produced in the coke oven gas desulfurization process with HPF method.On the one hand,its efflux or leakage would cause serious environmental damage.On the other hand,it contains ammonium thiocynate.Ammonium thiocyanate recovery and utilization are of great practical significance for coking enterprises.In this paper,the characteristics of DWS and the mixed salt were firstly studied.On this basis,an accurate method for determinating concentration of ammonium thiocyanate in mixed salts was established.The appropriate operating conditiongs of extracting ammonium thiocyanate from the mixed salt and the nature of the chromogenic substance in the extracted crude ammonium thiocyanate were also studied,And an efficient process of ammonium thiocyanate extraction and a method for purification and decolorization of the crude ammonium thiocyanate were developed.The main conclusions are as follows.Thermal analyzer and GC-MS analysis results showed that the main inorganics in DWS are ammonium thiocyanate,ammonium thiosulfate and ammonium sulfate,and the proportions of them in mixed salt are respectively about 50%,30%and 20%;organic matter are mainly phenols,nitrogenous and small amounts of alkanes,respectively accounted for 87.25%,11.54%and 1.21%of the total organic content.The applicabilities of bromine law,current Chinese national standard method(GB660-92)and spectrophotometric method for determinating of thiocyanate were discussed.The results indicated that bromine law was dangerous in the operation process;current Chinese national standard method was inaccurate becauses thiosulfate in DWS diaturbed the determination of thiocyanate and it caused great error in the process.While spectrophotometric method developed in this paper can determinate thiocyanate simply,accuratly and directly.While C(SCN-)<20?g.ml-1 and absorbance A<1,A and C(SCN-)met good linear relationship which chould expressed as A = 19.7272C-0.2774.It showed that leaching efficiency of leaching ammonium thiocyanate in the mixed salt increased along with the increase of liquid feed ratio,the times of extraction,the extraction temperature and the stirring speed,the reduction in the particle size of raw material.But the stirring speed and raw material particle size should be controlled to the optimum to reduce the difficulty of the subsequent solid-liquid separation.The intermittent process of leaching ammonium thiocyanate from the mixed salt complied with ln[C]s,0-4Cl,t(?-1)]-ln C s,0=-3/?Rtk1e-?E/RT,and the activation energys ?E were respectively 3.48kJ/mol and 2.67kJ/mol while the leaching solvent was]and 3.The chromogenic substance in crude thiocyanate ammonium contains eight elements-C,N,O,S,Hg,Ti,Bi and Po.They may form complexes with SCN-,or heterocyclic molecule complex with C,N,O and S.Among the four decolorization method,effect of chemical reaction is the optimal.A new effective ammonium thiocyanate decolorant NH was developed and the purity of ammonium thiocyanate after the purification and decolorization rised from 95.98%to about 99%.The product is white color and has achieved the index of First grade industrial product.In summary,this paper completed the studied of leaching and decolorition of ammonium thiocyanate from coking DWS.The purity of white product-ammonium thiocyanate is about 99%.The recovery of ammonium thiocyanate in the whole process is greater than 99%.The resource recycling of ammonium thiocyanate from DWS is accomplished. |
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