Treatment Of Thallium-containing FGS Wastewater By Coagulation Enhanced ZTI Clelator (CEZTI) And Its Engineering Practice

Desulfurization flue gas was released in the sintering process of raw ore and coal at iron and steel plant,which contained lead,zinc,thallium and other heavy metals.Thallium is a highly toxic and harmful substance,with a long-term cumulative toxic effect.Thallium pollution is enormous on public health.Due to the mature technology and large-scale application for removal of thallium in water is less,and desulfurization wastewater contains a large number of impurity ions,which greatly increased the difficulty of thallium removal.It is necessary to find an effective method for removing thallium from sintering wastewater.In this study,the method of "coagulation enhanced ZTI heavy metal chelator " was proposed to treat thallium in Flue Gas Desulfurization（FGS）wastewater.This technology was successfully applied to a 1200 m³/d FGS wastewater upgrading project in steel plant in Guangdong.The coagulant is FeSO₄ and PAC,and the heavy metal chelator is self-developed ZTI chelator.Summarization of technique characteristics,impact factors,optimization of operation and economic evaluation could promote the upgrade of thallium-containing FGS wastewater treatment using the ZTItechnique.Laboratory and pilot tests were used for the thallium-containing FGS wastewater treatment by using the ZTI technique.The results showed that the ZTItechnique can remove thallium and other heavy metals at the same time,such as arsenic,copper,cadmium,lead and zinc.The method of “coagulation + ZTI chelator” is better than that of “ZTI chelator +coagulation” in dealing with thallium-containing FGS wastewater.The thallium content in effluent was less than 0.005mg/L of emission standards.The ZTI technique was used for emergency production test of thallium-containing FGS wastewater.At first,the coagulant PAC and FeSO₄ were added to remove part of the pollutants,reducing the pollutant load of the follow-up process.Three different proportion ZTI chelators（0.9mL/L A,12.2g/L B and 12.2g/L C）were then added into the wastewater,respectively.After the insolubles were formed in 10-30 min,solid-liquid separation was carried out.The results showed that the thallium concentration of effluent was 0.1-4.65μg/L,which was less than 0.005mg/L of emission standards.The concentration of zinc,lead,cadmium,copper and arsenic were 0.066,0.0094,0.00012,0.010 and 0.010mg/L,respectively.It is indicated that the method can remove thallium and other heavy metal ions simultaneously,and the insoluble matter precipitates fast and is easy to be separated.The ZTI technique was applied to a 1200 m³/d FGS wastewater upgrading project in steel plant in Guangdong.The operating results of demonstration project showed that,the average concentration of COD_Cr,NH₃-N,thallium,zinc,lead,cadmium,copper and arsenic were 423.36,24.47,0.00421,1.12,0.84,0.06,0.03 and 0.38 mg/L,which meet their emission standards respectively.The reduction quantity of COD_Cr,NH₃-N and thallium were 687.18,188.47 and 0.50t/a,respectively.The characteristics of the ZTI technique in the application of upgrading wastewater treatment include high quality of effluent,less cover area,strong impact resistance,auto and simple operation.The unit investment for ZTI technique was calculated,including operational fee of 5.3484 million per year,and 12.21 Yuan per ton of wastewater.The thallium-containing FGS wastewater could meet the wastewater discharge standards after treating with the ZTI technique and the investment and operating costs was relatively low.