Effect Of Sulfur On Soliditiction Distribution Of Heavy Metals In Cement Clinker And Clinker Mineral Composition

Tailing,a kind of solid waste derived from mineral resources processing,contains heavy metals such as lead,zinc,cadmium and chromium,which may cause harm to the ecological environment and human health without proper treatment.Cement kiln collaborative disposal is seen as one of the effective ways to recycle tailing,but the enrichment of sulfur in the cement kiln may affect the solidification and distribution of heavy metals and the mineral composition of clinker.In this paper,ICP-OES,SEM-EDS,XRD Rietveld,structural difference factor and other analysis methods were applied to investigate the solidification and distribution of Pb,Zn,Sn and Ti in the clinker with the different sulfur contents.The capability of Pb,Zn,Sn and Ti to substitute ions(Ca²⁺,Si⁴⁺,Al³⁺and Fe³⁺)was also analyzed in the clinker after incorporating FeS.In addition,the effects of mineral compositions in clinker on the capability to solidify heavy metals were determined to reveal the solidification and distribution mechanism of heavy metals under the influence of sulfur.The main conclusions are as follows:（1）With the increase of sulfur content in clinker,the solidification rate of Pb increased by 5.56～22.40%,but that of Zn decreased by 1.22～4.30%,and that of Sn and Ti did not vary significantly.Pb,Zn,Sn and Ti were still mainly distributed in the intermediate phase.Specially,the content of Zn increased by 3.49～13.71%in the intermediate phase when Zn was transferred from silicate phase to intermidate phase.Ti was transferred from intermediate phase to silicate phase,so that its content increased by 5.81～32.04%in silicate phase.Meanwhile,the content of Pb increased in both silicate phase and intermediate phase,but more in the intermediate phase（113.67～307.09%）,while that of Sn remained almost unchanged in each mineral phase.（2）The chemical valence of Pb,Zn and Ti did not change with the incorporation of FeS,except that Sn⁴⁺was partly reduced to Sn²⁺.Notably,the incorporation of FeS enhanced possibly the capability of Pb²⁺to substitute Ca²⁺in C₃A and C₄AF as well as that of Zn²⁺to substitute Al³⁺in C₃A,and that of Ti⁴⁺to substitute Ca²⁺or Si⁴⁺in C₂S.（3）The content of Fe²⁺and Ca SO₄ increased with the increase of FeS incorporation in the clinker,resulting in a decrease in C₃S content and an increase of C₂S and f-Ca O content.Especially,the content of C₃S decreased to about15.0 wt.%in clinker when the content of FeS increased to 1.4 wt.%For the clinker containing Pb or Zn,the formation of Ca₄Al₆O₁₂SO₄ and Ca₃Al₄Zn O₁₀was promoted by FeS,causing a reduction in C₃A and C₄AF content.（4）The capability of the intermediate phase to solidify Pb and Zn was improved by the formation of Ca₄Al₆O₁₂SO₄ and Ca₃Al₄Zn O₁₀ in the clinker.The incorporation of FeS forces Ti⁴⁺into theα-C₂S crystal lattice,and thus expands the spascing（2.7115 nm→2.7125 nm→2.7134 nm→2.7149 nm→2.7168 nm）of betweenα-C₂S cerstal planes,thereby strengthening the capability of silicate phase to solidify Zn.