A Pilot Research On The Treatment Of Industrial Waste Gas Containing Cyanide With Chemical Absorption And Ionizing Radiation Technology

Polyacrylonitrile-based carbon fiber （PANCF） produces large amount of harmfulemissions in the production process, in which hydrogen cyanide （HCN^-） is a verypoisonous substance that belongs to the refractory compounds. Pilot experiments werecarried out to treat the real cyanide-containing waste gas produced from a carbon fiberenterprise in Jiangsu province using NaOH and NaClO as the absorbing liquid. Thenthe residual cyanide aqueous solution was introduced into a process vessel andirradiated by a self-sheltered Dynamitron electron accelerator （energy0.5¹.0MeV,beam current10¹5mA） to transforme the CN^-into non-toxic or low poisonouscompounds. The cyanide containing waste gas and wastewater processing capacitywere8000¹5000m³/h and10³0t/d, respectively. At the same time, the operatingconditions for absorption and irradiation had also been optimized.Results showed that both NaOH and NaClO were effective to eliminate the HCN^-from waste gas. When the absorbent was NaOH, we need to guarantee absorptiontower pH>12, pay attention to the recycling of high concentration cyanide wastewaterin the first absorption tower, and ensure continuous processing low concentrationcyanide wastewater in the secondary absorption tower. While the absorbent wasNaClO, we need to guarantee the active chlorine in the tower was more than1%. Atthe same time, determine NaClO dosing quantity according to the exhaust gas flowand HCN^-concentration, and guarantee the continuity of dosing. During the treatment,the first absorption tower pH should control above11and the second absorption towerpH should control between9¹1. Or there will lead to CN^-Cl gas generation when thepH<10. And it was not conducive for the HCN^-gas absorption.Radiation technology was also effective for removing cyanide from wastewater.When CN^-concentration was21.08¹17.49mg/L, absorbed dose was1.5kGy, theCN^-removal efficiency was between33.88⁵9.25%. The combination of radiationand O₃remarkably increased the degradation efficiency of cyanide. In the presence of2mg/L O₃, the CN^-removal efficiency increased to48.19⁸2.62%at the sameabsorbed dose. However, due to the presence of carbonates, experimental resultsfound no radiation-ozone’s unique “synergy”. The decomposition rate of the cyanidecould be described by pseudo first-order kinetics model. Ammonia and cyanate wereidentified as the main intermediate nitrogen-containing products.Through this pilot, we can see that NaOH/NaClO absorption and ionizing radiation technology was a viable option for cyanide-containing waste gas andwastewater treatment. But the process still have some difficulty in large-scalepromotion, especially the ionizing radiation technology application in the field ofenvironmental protection. To our knowledge, this pilot study is the first example forreal industrial wastewater treatment using continuous irradiation by electronaccelerator, which provided a good demonstration for applying ionizing radiationtechnology for wastewater treatment in China.