Experimental Study On Wastewater With Chromium From Jianlong Extracting Process Of Vanadium By Chemical Precipitation Method

With the development of science and technology,the scale of heavy metal wastewater entering the environment continues increasing every year.If we can not solve the problem,effectively,it will pose great damage to the environment.At the meaning time,per capita water resources is one of the poorest countries in China,and water problem is a burning question.It is easy to collect in body for pollution,especially heavy metals.These elements,which were absorbed into body,will break the balance of normal metabolism and even cause cancer.There are many different valences of chromium in the water environment,mainly including hexavalent chromium and trivalent chromium.Hexavalent chromium,one of the ruling elements(Hg,Cd,Pb,Cr and As),is much toxic,which is known as a carcinogen.Trivalent chromium is not toxic,which is a necessary element for human beings.There are many efficient methods for the chromium wastewater treatment,such as chemical method,biological method,Electrolysis method and so on.This paper adopted chemical precipitation process to deal with the high chromium wastewater of vanadium extracting process from Jianlong.(1)The removal high chromium wastewater of vanadium extracting process from Jianlong was studied by chemical precipitation method.The reduction effects of organic reducing agents(cellulose,glucose)and inorganic reducing agents(Na2S2O3,Na2SO3,and Na2S2O5)on the hexavalent chromium made a preliminary inquiry.(2)In this experiment,the reaction conditions were controlled,which included the pH under the reducing conditions,the pH under the precipitation conditions,the reaction time,and the amount of the reducing agent.Under the condition that the wastewater treatment results met the national emission standard,the reaction conditions were optimized.Finally,the reducing agent and the optimum process conditions were determined.Experimental results showed these phenomenon.The theoretical pH of the three reducing agents was less than 4.0.Because the initial pH of the wastewater is 2.4,there is no need to adjust the acidity of the wastewater under the reducing conditions.The pH under precipitation conditions of reducing agents were about 8.5,and the precipitation effect is the best.When the amount of sodium thiosulfate is more twice than the theoretical value,and the amount of sodium sulfite is twice the theoretical value,and the amount of sodium metabisulfite is 7.0 times theoretical value,the reduction effects reached the best level respectively.From the efficiency point of view,the time of the reduction reaction reached 30min,there was no practical significance to continue.(3)Through a series of experiments and comparative analysis,sodium sulfite was the best reducing agent.The cost of treatment of 1m3 wastewater was 4.01 yuan,the removal rate of hexavalent chromium reached 99.89%,the content of Cr(Ⅵ)was 0.304 mg/L,the total of chromium content was 1.208 mg/L.The cost of Sodium pyrosulfite and sodium thiosulfate 5.50 yuan and 4.24 yuan,respectively.The water quality both met the national emission standards(GB8978-1996).(4)In order to control the amount of sludge,sodium hydroxide solution was used as a neutralizing agent in the precipitation reaction.After the reducing agent reduces hexavalent chromium to trivalent chromium,the pH was adjusted to form a precipitate of chromium hydroxide.