Research Of Comprehensiveutilization Technology On The Chromate Mother Liquor Reduced By Starch

The process of chromic oxide(Cr2O3) preparation under hydrothermal conditions has a lot of advantages. The by-product of this process is reduced mother liquor, which contains large amounts of carbonates and organics and a little Cr(VI). Some treatments are conducted on the mother liquor and it is converted into inorganic salt products. This process reduces the waste stream, increases the productivity effect, and achieves the comprhensive utilization of the resources.In the research of chromium removal from potassium chromate reduced mother liquor and productization, the optimal conditions of chromium reduction and flocculation in alkaline environment were studied, and the preparation contitions of K2CO3 products were explored as well. The results show that the optimum conditions of potassium chromate reduced mother liquor treatment are determined to be an addition of hydrazine hydrate in a molar ratio of N2H4 to Cr(VI) of 2.25, a reduction time of 20 min, and a reduction temperature of 60℃. An anionic polyacrylamide(APAM) is adopted as the optimal flocculant. The optimum flocculation conditions are as follows: a flocculation temperature of 60℃, a flocculation time of 3h, and a flocculant amount of 4mg/L. The filtrate should be evaporated to the mass fraction of K2CO3 reached 31%~34%. In addition, pressure, time, teperature and stirring speed should be 0.8 MPa, 3 hours, 50℃ and 600 r/min in carbonation, respectively. Meanwhile, the carbonized KHCO3 is calcinated at 650℃ for 2 hours. Under such conditions, the content of K2CO3 in products reaches 99.65%, which are up to the national standard.In this paper, scanning electron microscopy, energy-dispersive spectroscopy, Fourier-trasform infrared, Raman, X-ray diffraction, ultraviolet-visible spectrscopy and mass spectrometry were performed to analyze the reduced mother liquor and reduzate, and the removal mechanism of chromium was discussed. The characterizations show the existence of a kind of organic containing 3, 5–dicarbonyl–6–hydroxyhexanal. According to the analysis and the structure of starch, the process of chromium removal is inferred. The key component of the precipitation is the complexation between the Cr(III) ions and 3, 5–dicarbonyl–6–hydroxyhexanal, which has octahedral and six-coordinated structure.The application of sodium chromate reduced mother liquor in the treatment of chromium-containing sodium hydrogen sulfate was studied, the optimal conditions of chromium reduction and precipitation were obtained, and and the preparation contitions of Na2SO4 products were explored as well. The results show that the optimum conditions of potassium sodium reduced mother liquor treatment are determined to be a reduction time of 10 min, a reduction temperature of 20℃, a reduction p H value of 2~3, and an addition of sodium pyrosulfite in a molar ratio of Na2S2O5 to Cr(VI) of 0.825. The precipitation temperature, p H value and time are 20℃, 7~8 and 40 min, respectively. The calcination temperature and time are 650℃ and 2 hours. Under such conditions, the content of Na2SO4 in products reaches 99.34%, and the chromium content is below 0.005%, which meets the quality standard requirements.