The Preparation Of Phosphorous Slag-based Alkali-activated Cementitious Materials And The Basic Research On Solidified Arsenic-calcium Slag

Arsenic is a sulphur-like metalloid element existed with lead,copper,nickel,zinc,tin and other non-ferrous metals natural minerals.And it is gradually enriched in the mining,selection and smelting process of non-ferrous metals.In these process,arsenic is dispersed into waste water,waste residue and dust in various ways,and finally it would form arsenic-containing waste slags such as arsenic dust,calcium arsenate waste and sulfur arsenic slag with different arsenic content.As₂O₃ and derivative compounds contained in above arsenic-containing waste slags are easy to leach arsenic in the stockpiling process.Therefore,it must be treated by solidification/stabilization technology.Based on above consideration,this paper proposed to use phosphorus slag?PS?as the main raw material,combined with blast furnace slag?BFS?,calcium hydroxide?CH?and the compound activator?CA??sodium hydroxide,water glass,sodium sulfate,sodium chloride?,to prepare phosphorus slag-based alkali-activated cementitious materials,and it was regarded as a solidified matrix material to solidify calcium arsenate waste.Meanwhile,the formation mechanism of phosphorus slag-based alkali-activated cementitious materials and its solidification mechanism of arsenic was researched.The results and conclusions of this study was summarized as follows:?1?The compressive strength of specimens could reach 46.0 MPa and 43.3 MPa,respectively,when the phosphorus slag/slag mass ratio was 7:2,the cement content was 10%or the calcium hydroxide content was 4%under the steam curing condition.?2?When calcium hydroxide was equal to 70:20:4,the optimum proportion of the compound chemical activator were NaOH 0.15%,NaCl 0.2%,Na₂SO₄0.5%and water glass0.3%.The compressive strength of specimens can reach up to 66.9 MPa and increased 56%compared to the sample without compound chemical admixture.?3?The analytical results of XRD,FT-IR,SEM/EDS and TG-DTG showed that the main hydration products of cementitious materials were C-S-H and C-A-S-H gels.The addition of compound chemical activator could improve the hydration reaction degree of cementitious materials and significantly increased the compressive strength of specimens.?4?The optimum ratio of arsenic solidified body was consisted of 6:3phosphorus slag/slag,4%calcium hydroxide and chemical activator was 2%;Under this condition,the compressive strength of the solidified body was up to 78.75 MPa,the arsenic leaching concentration was 1.04 mg/L,the initial setting time was 70 min and the solidification capacity of calcium arsenate waste was 40%.?5?The hydration mechanism of phosphorus slag-based alkali-activated cementitious materials for solidifying calcium arsenate waste includes two aspects:on the one hand,the sparingly soluble CaHAsO₄·3H₂O transformed into more stable Ca₅?AsO₄?₃OH or the isomorphous Ca₅?AsO₄?₃?OH,F?compounds;on the other hand,the arsenic could be absorbed and enclosed by the three-dimensional structure of hydration products.