To Optimize Process Of Arsenic Removal Of Ferric Chloride Flocculation In Yangzonghai Arsenic Pollution

Arsenic and its compounds are common pollutant with toxicity and carcinogenicity. The pollutant caused by arsenic has caused people’s attention. Thus, research on arsenic removal technique has important practical significance. In this paper, we selected kinds of flocculants or adsorbents in order to find out better arsenic removal technique based on the case of dealing with Yangzonghai Lake arsenic pollutants. FeCl3 flocculation was concluded to be a suitable technique for arsenic removal in Yangzonghai Lake. Besides, practical problems faced by project arsenic removal test in Yangzonghai Lake were solved, some improving plans were put forward, and mechanism of arsenic removal using FeCl3 was investigated further.Different flocculant/adsorbent dosage, pH, stirring time on arsenic removal rate using FeCl3 were studied. The results showed that the better Fe/As molar ratio was 7.15:1 and the better stirring time was 5 min. Arsenic removal rate in Yangzonghai Lake 3# spring would be above 95% in this condition. FeCl3 flocculation was the best method for arsenic removal in Yangzonghai Lake 3# spring. It was attributed to this method suited for large range of pH and was not easily affected by stirring time.Stirring time, dosage of FeCl3 and initial concentration of arsenic were studied in arsenic removal to discuss the effect of FeCl3 in different systems. Under conditions of [As] 100.0 μg·L-1, mole ratio of Fe/As 30.8:1, stirring 5 minutes, arsenic(Ⅲ) and arsenic(Ⅴ) removal rate in deionized water were 85% and 98% respectively, while arsenic(Ⅲ) and arsenic(Ⅴ) removal rate in Yangzonghai Lake water were 75% and 90% respectively.Influence of HCO3- and Ca2+ in Yangzonghai Lake water on arsenic removal was investigated. The results showed that arsenic (Ⅲ) and arsenic (Ⅴ) removal rate in deionized water were above 80% and 95% respectively under the condition of common influence of HCO3- and Ca2+.Influence of the main components in Yangzonghai Lake water for stability of Fe/As precipitate in sediment was studied by research on effection of the existence of HCO3- and Ca2+ for the desorption of fresh Fe/As precipitate and sediment. The results showed that desorption of fresh Fe/As precipitate stabilized at low level under the condition of mutual impact of HCO3- and Ca2+. HCO3- resulted in arsenic desorption in sediment only 0.1%. It means that arsenic would not be released.