Study On The Removal Effect And Mechanism Of Antimony And Arsenic In Acid Mining Drainage By Carbonate Rock Combined With AMD Iron Flocs

Mining development produces direct untreated discharge of acid mine wastewater with low pH,high SO₄^2-and high Fe content,acidizing easily downstream water and affecting seriously ion migration and transformation.Especially in Guizhou province,possesses rich antimony and arsenic mineral resources,numerous and scattered,and the waste water is not easy to be centralized treated.At present,people use mainly absorbents to treat the waste water,such as absorption of zero-valent iron,modified biomass carbon and so on in the world.However,there is little research on passive treatment of antimony wastewater by carbonate rock.Researchers mainly focused on the passive treatment AMD high-concentration iron,manganese and sulfate.When it comes to benefit,the existing adsorbents are difficult to meet the water quality requirements.Therefore,in order to seek an economically feasible,practical and efficient treatment method for acid mine drainage,this paper attempts to treat acid mine drainage by regarding iron,antimony and arsenic with AMD iron flocs and carbonate rocks widely distributed in southwestern China as the main reaction medium.A series of work has been carried out,and some results have been obtained as follows:1.The neutralization reaction between the iron-free aqueous solution and the carbonate rock has no obvious effect is not notable on the removal of As and Sb.After the iron-containing aqueous solution neutralized by the carbonate rock,it can induce the co-precipitation of Fe,Sb and As to be removed from the water,and its effection will also improve as the concentration of Fe levels up.Under typical acid-base conditions(pH=3?9),the release of AMD iron flocs to Fe will decrease with the increase of pH value,but the release of Sb(?)and As(?)dose not.AMD iron flocs is more stable in neutral or weak alkali environment.2.The acidic conditions are more favorable for the adsorption of Sb(?)?As(?)AMD iron flocs.Under acidic conditions(25?,pH=6),the maximum fitting adsorption capacity of Sb(?)is 6.784 mg/g,and the maximum fitting adsorption capacity of As(?)is 20.23 mg/g.The removal of Sb and As is mainly achieved by the complexation and coordination of iron oxides,and the adsorption process has the characteristic of irregular distribution of effective adsorption sites.Under the influence of the mixed system,As has a stronger binding force than Sb.3.The longer the hydraulic retention time,the more favorable the carbonate rock will improve the AMD pH.It will aid in removing the As and Sb and oxydrolysising more AMD iron flocs.As(?)is easier to be removed than Sb(?)under different hydraulic retention time.4.In two series systems,the 1#system(net filled carbonate rock)and the 2#system(combined carbonate with AMD iron flocs)can enhance the effective pH.The neutralization mainly depends on the stable and lasting alkali release of carbonate rock.Under the environment of low pH value,AMD iron flocs can effectively adsorb and remove As(?)?Sb(?).In the early stage of 1#,2#system operation,Fe,Sb and As are mainly removed by the reaction medium at the front of the system.After running for 30 d,the metal ions in AMD are mainly removed by the neutralization reaction at the back of the system to form a precipitate in the 2#system.In general,the effect of 1#system on metal removal gradually increases with the time prolongs.Fe removal rate is close to 100%,while Sb and As removal rates are around 76%and93%respectively;The 2#system's metal removal effect gradually weakened with the time prolongs,the Fe removal rate reached 98%,while the Sb and As removal rates were around 80%and 90%,respectively.5.After the carbonate rock happened neutralization in the vertical flow-parallel flow series system,a layer of AMD iron flocs filter membrane with goethite,lepidocrocite and gypsum as the main mineral phases that can adsorb heavy metals is formed on its surface.And the AMD iron flocs deposited in the device mainly composed of unshaped hydrated iron oxides with poor crystallinity such as goethite and lepidocrocite,which are mainly precipitated in a flocculent structure,which has a good adsorption effect on metal ions.