Harmful Components Separate From Stainless Steel Slag Used For Fertilizer Raw Materials

As a by-product of stainless steel smelting process,stainless steel slag contains a large number of nutrients element that beneficial to the soil and the growth of crops,so it can be used for fertilizer raw materials.In view of this application,the mineral phase characteristics of stainless steel EAF slag were studied,the factors that restrict the use of stainless steel as silicate fertilizer raw materials were the Cr content.According to the magnetic properties of two kinds of chromium mineral,two step magnetic separation process is used to eliminate the chromium mineral.Using alkaline roasting-water leaching to treat magnetic tailings,the content of Cr in final slag can meet the requirements indicator of silicate fertilizer raw materials.The results show that the mineral composition of EAF slag is ?-Ca₂SiO₄??-C₂S?,merwinite?Ca₃Mg?SiO₄?2?,dicalcium ferrite?Ca₂Fe₂O₅?,gehlenite?Ca₂AlSi₂O₇?,Fe-Cr-Ni alloy,RO phase,magnesiochromite?MgCr₂O₄?and maghemite?Fe2O₃?,which the mineral contains chromium is Fe-Cr-Ni alloy and magnesium.The size of these 2 minerals in EAF slag was 12-102?m and 11-46?m respectively,and the volume fraction was 7.8%.The indicators of stainless steel slag are in line with NY/T 797-2004 “silicate fertilizer”,but the chromium content in the stainless steel slag is 19.4 times of the national standard GB/T 23349-2009 “Ecological index of arsenic,cadmium,lead,chromium and mercury for fertilizers” requirements,other 4 kinds of heavy metals harmful components?arsenic,cadmium lead,mercury?were not detected in the stainless steel slag.Using the magnetic flux density of 180 mT weak magnetic separate the stainless steel slag,the yield of the concentrate is 6.6%,and the content of Cr in the tailings is reduced by 10.2%.Using the magnetic flux density of 1200 mT strong magnetic separate the tailings of weak magnetic separation,the yield of the concentrate is 49.2%,and the content of Cr in the tailings is reduced by 36%.The content of Cr in the tailings after magnetic separation is 0.56%,higher than the standard GB/T 23349-2009 limit value of 10 times.Tailings after magnetic separation were treated by alkaline roasting water leaching method,3g stainless steel slag,NaOH 1.5g,NaNO₃ 0.2g,roasting temperature 400? and roasting time 2h.The content of chromium in the residue was reduced by 91.7% after roasting,Ca and Mg increased by 10.8% and 12.5% respectively,and Si decreased by 7.2%.After the treatment of two step magnetic separation?weak magnetic separation,high intensity magnetic separation?,roasting-water leaching,the content of various elements in stainless steel slag can reach the national standard GB/T 23349-2009 value limit requirements of technical indicators,meet the used as silicate fertilizer raw material requirements.