Phosphorus Wastewater Of Iodine Recovery And Purification Of Research

Iodine exists in yellow phosphorus wastewater mainly as iodide ion. Based on the character of wastewater which is high in iodine but weak in acidity, In this article, iodine is separated and abstracted by the air-out method, and defluorination technology of the iodine absorption liquid is discussed deeply as well. It has an importance meaning to study the extraction and purification technology of iodine for achieving comprehensive utilization and efficient utilization of phosphorus mineral resource in our province.Test results show that the concentration range of iodine ,fluoride in yellow phosphorus wastewater are 60 - 140 mg/l, 500-800mg/l respectively, while pH 4.6-5.2. Much research work has been done by predecessors in recovering low concentration iodine and also a lot of achievements were obtained, but they were just in experimental stage because of complicated technology, high cost and high fluoride content in product.Extraction by using air is used to separate and abstract iodine from yellow phosphorus wastewater in this method. Extraction process includes: acidizing with sulphuric acid; oxidizing and separation; reducing and absorption. The process was simple, lower cost and easy to industrialize. Experimental results: the extraction rate and the absorption rate of iodine both are over 90%; Total recovery rate is more than 80%, fluorine accumulation in sample iodine is less than 1mg/kg, while the contents of impurity elements of Pb,Hg and As come up to the purification standard.Experiments were scheduled by orthogonal design method to optimize the extraction conditions of the iodine. The results showed that absorbing temperature, the amount of oxidant and gas/liquid ratio had important influence on recovery, and absorbing temperature had the most significant influence. Under the condition of the pH value of the acidified liquid 1 or so, to investigate the recovery of iodine by the air extraction method, Optimum technology conditions of recovering iodine from yellow phosphorus wastewater by air-out method(volume of the yellow phosphorus wastewater is 2000ml)is as follows: Absorbing temperature: 35℃;Amount of oxidant: 15ml;Gas/liquid ratio: 150-200:1;Oxidation time: 4min;Recovery of iodine is more than 80% under optimum technology conditions. Research shows that the mathematic equation is obtained between the recovery of iodine and the former three factors as following:η= 79.0455+(-0.225 1X₁² + 16.20742X₁ -287.8001) +(-0.144887X₂² +4.39304X₂ - 29.919)+(-0.00022X₃² +0.12951X₃ -18.47285)It is evitable for the crude iodine to hold some harmful impurity elements of Pb, Hg, As and F because phosphate rock contain a lot of metallic and nonmetallic impurities, which results in the value of application decrease greatly. Compared with various defluorination process, experimental research on defluorination technology for absorption liquid with high concentration iodine in the recovery process by air extraction is also done. Two-stage Sedimentation coagulation method were selected for the defluorination and purification: The residue of fluoride was decreased to 60mg/l or less after the iodine solution had been treated to take off fluorine with lime at first, and treated with aluminum salt to further take off fluorine under the pH 6-7condition, the fluoride concentration in wastewater is lowered to 10mg/l or less, fluorine accumulation is ensured under 1 mg/kg. High purity iodine was attained after clean liquid had been oxidized, the purity of the product was over 99.5% while the lowest concentration of fluoride was lower than 0.5mg/kg, and those of Pb,Hg and As were lower than 1 mg/kg.The experimental regressive model about the relationship between the used amount of aluminum salt and the concentration of fluorides in the wastewater can be described as:Y = 0.9683 + 0.0272X - 2×10^-5X²...