Study On Solidification/Stabilization Technology Of Arsenic Contaminated Soils Using Molysite And Quicklime

Arsenic is an element that is widely distributed in the earth's crust. Arsenic and its compounds have widely used in the productions of alloy,dyes,pesticides,preservatives and so on. With the development of arsenic industries,leakage - fire - explosion of chemicals containing arsenic may happen at times,which would easily induce serious environmental pollution accident. Once it happens, environment and peoples may suffer a lot. Due to the high toxicity of arsenic, it,s necessary to adopt emergent measures to control pollution after the accident. Contaminated sites need to be quick remedied, so as to reduce the pollution degree and pollution range to the minimum.In this paper,arsenic contaminated soils were recognized as the research object,which contained two categories. One was collected from Haidian district in Beijing,denoted by HD,the other was from Shenyang smelter polluted by arsenic and other heavy metals,denoted by,SY having SY-1,SY-4 and SY-5 three kinds of soils. In-situ chemical solidification/stabilization(S/S)was used to remedy the contaminated soils and ferrous sulfate,ferric chloride,polymeric ferric sulfate were chose as the main agent for S/S. At the same time,a probe into the S/S effects of three materials came from two aspects- solidification/stabilization efficiency(denoted by SE) and leachate content(denoted by LC).The following conclusions were drawn:(1)With the increasing of Fe/As molar ratio,S/S effects of three agents become better. As to soil HD,when FeSO4,FeCl3,PFS were added in it according to Fe/As molar ratio 6,3,125,SE can exceeded 90% and LC can deceased to 5 mg/L below(.2)When SY-1 and SY-5 with he pH value of 6.92 and 4.19 respectively were adjusted to 11.14 and 9.07 using quick lime,SE of FeSO4 and FeCl3 to arsenic can obtain rise to 91.11% and 99.47%,having LC 3.17 mg/L and 1.06mg/L simultaneously.(3)As to soil HD and SY-1 and SY-5 having been adjusted pH,after one day of cure time,both of ferrous sulfate and ferric chloride had the SE of above 99%,and the arsenic in leachate would dropped 1mg/L below. Because of hygroscopicity PFS had,in lower soil: solution ratio circumstance,chemical reaction progress between PFS and arsenic become slowly. Generally,insoluble arsenic-bearing phases formed gradually just after 2~5 days. Therefore,similar to this point,SY-1 using PFS as S/S reagent acquired the preferable effects after 5 days,curing. But SE only reached 88.66%,LC remained higher more than 8.06mg/L.(4)Because SY had the higher content of competitive ions,such as sulfate(SO42-),phosphate(PO43-),zinc ion(Zn2+) and (Ca2+),with the cross interference by Cd,Pb,Hg,Cu and other kinds of metal elements simultaneously,three curing reagents in it performed much poorer Especially,as to SY-4,ferric chloride owned the best performance but only with the results of 40.39% and 58.72mg/L.Therefore,combined use of solidification/stabilization reagent must be considered.