METHOD AND INSTRUMENT FOR MEASURING CONCENTRATION OF RESIDUAL HEXAVALENT CHROMIUM ION IN WASTE WATER SUBJECTED TO REDUCTION TREATMENT

摘要

PURPOSE:To continuously and exactly measure the concn. of Cr6+ by adding iodine to 1st test water sampled from waste water subjected to a reduction treatment to the extent that the water develops a slight color, setting the ratio of the required iodine quantity, oxidizing the excessive Na2SO3 component to form 2nd test water, and measuring the remaining Cr6+. CONSTITUTION:The waste water subjected to the reduction treatment in a reducing vessel 2 is fed into a sample tank 3 and the 1st test water sampled from the sample tank 3 is sent to a pH adjusting vessel 4. The 1st test water is adjusted to alkalinity of 9 to 11 pH and thereafter, the iodine is added as an oxidizing agent to the extent that the 1st test water develops the slight color. The ratio of 80 to 90% of the iodine quantity to be added is set as the iodine quantity necessary for oxidizing the excess Na2SO3 component remaining in the waste water subjected to the reduction treatment. On the other hand, the set iodine quantity is added to the 1st test water subjected to the pH adjustment to oxidize the excess Na2SO3 component. This test water is used as the 2nd test water. The concn. of the cr6+ remaining in the 2nd test water is measured by a diphenyl carbazide absorption photometric method.