1、Baosteel Technical Research Volume 3, number 4, December 2009 , page 14 Beneficial use of stainless steel EAF slag as composite cement admixture and its heavy metals leaching risk analysis WANG Ruyi , CHEN Ronghuan and SHI Lei Environment & Resources Division, Research Institute, Baoshan Iron & Stee
2、l Co., Ltd., Shanghai 201900, China Abstract: This study analyzes the feasibility of using stainless steel electric arc furnace ( EAF ) slag as composite cement admixture and the risk of leaching-out of heavy metals. The results show that the stain less steel EAF slag, mainly made up of Ca2SiO4, Ca3
3、Mg(SiO4)2, some Cr-containing minerals and in small particle size, is easily ground and has cementitious activity. EAF slag, w hen used as cement admixture, can be added with a maximum percentage of 32%. It can meet the strength requirements of the standard PC 32.5 cement When the mixing percentage
4、is decreased to 25%, the strength o f the cement can be increased to that of PC 42.5 cement Other main quality indexes of composite cement such as the setting time and stability, also satisfy standard requirements. The results also show that most o f the heavy metals in the stainless steel EAF slag
5、exist in a stable speciation. The concentration of heavy metals that leach out from the stainless steel EAF slag and the composite cement products is far lower than the standard limit of hazardous wastes. The m a in heavy metal chromium, exists as less hazardous trivalent chromium. Therefore, the ri
6、sk of heavy metals leaching out from the stain less steel EAF slag is low. The internal expo sure index (IR) and the external exposure index (I) of the stainless steel EAF slag are both lower than 1. 0, satisfying the standard requirements of the state for the radionuclides of building materials. Th
7、erefore, stainless steel EAF slag can be safely used as admixture to produce composite cement Key words: stainless steel EAF slag； composite cement admixture； heavy metal； risk of leaching out 1 Introduction The annual stain less steel slag output has topped 3 Mt in China, and how to effectively pro
8、cess the slag has become an emerging issue. The chemical and mineral compositions of stain less steel slag are similar to those of Portland cement and blast furnace (BF) slag, which are conventionally used as the raw material for cement Therefore, it is believed that stain less steel slag can be use
9、d as a raw material for cement Since stainless steel slag contains chromium oxide and other heavy metals, its effect on the environment should be clarified when it is used as a resource. In this study, stainless steel electric arc furnace (EAF) slag, with the biggest output and highest chromium cont
10、ent in stainless steel slag, was the main focus of research. By testing the chemical and mineral compositions, the radioactivity, the cementitious activity, the heavy metal leaching toxicology and the performance of the composite cement the feasibility of the use of stain less steel EAF slag as comp
11、osite cement admixture and the risk o f heavy metals leaching out were analyzed, in order to provide grounds for using stainless steel slag as a safe resource. 2 Material and methods The stain less steel EAF slag w as sampled from the Baosteel Stainless Steel Business Unit It was the tailings of mol
12、ten stainless slag from an EAF after water immersion, cooling, crashing, grinding, and gravity and magnetic separation. The chemical and mineral compositions of the stainless steel EAF slag were determined using an X-ray fluorescence spectrometer ( referred to as XRF, Model SRS 3400, produced by BRU
13、KER AXS GMBH, Germany) and an X-ray diffractometer ( referred to as XRD , Model D /max 2550X, produced by Rigaku Co.,Japan) . The contents of Cd , Cr, Cu, Ni Ba , Pb , and Zn in the slag sample were analyzed by ICP-OES ( Optima 2100DV, produced by Perk in Elmer Inc., USA ) , while the contents of As
14、 and Hg were analyzed by AFS ( XGY1012, produced by the Institute of Geophysical and Geochemical Exploration, the Chinese Academy of Geological Sciences, China ), after aquaregia digestion. The concentration of Cr (VI) in the leachate was determined by Dipehenylcarbohydrazide Spectrophoto-metry . Th
15、e leaching toxicity of the slag samples was determined according to the Test method standard for leaching toxicity of solid wastes. the horizontal vibration extraction procedure(GB 5086. 2-1997) and the Toxicity Characteristics Leaching Procedure ( referred to as TCLP, USA ). The speciation of heavy
16、 metals in the slag samples was analyzed by the sequential extraction procedure according to the Tessier A and Wan X method. Internal and external exposure indexes were determined accord ing to the state standard, the Limit of radionuclides in building materials ( GB 6566- 2001). The cementitious ac
17、tivity test of the EAF slag was determined according to the Test method for the activity of industrial waste slag used as cement mixing materials (GB 12957). The compressive and bending strength of the cement were determined according to the Test method for cement mortar strength (ISO) (GB/T 17671-1
18、999). The consistency, setting time and soundness of the cement were determined according to the Test methods for the water consumption, setting time and the stability of the normal consistency of Portland cements (GB/T 1346-2001). 3 Results and discussion 3. 1 The physical and chemical properties o
19、f the stainless steel EAF slag Table 1 shows the chemical composition of the stainless steel EAF slag. The slag is mainly made up of CaO, SiO2, Al2O3, MgO, and contains less Fe, more SiO2, a higher concentration of Cr2O3 and some NiO when compared with conventional carbon steel slag. The mineralogic
20、al result (Fig.1) indicates that stainless EAF slag contains silicates, i. e., Ca2SiO4, Ca3Mg(SiO4)2, and Cr containing minerals. The chemical and mineral properties o f EAF slag are similar to those of cement suggesting that stainless steel slag can be used as a raw material of cement 3.2 The heavy
21、 metal content in stainless steel EAF slag and the leaching toxicity of the slag The heavy metal content in stainless steel EAF slag are shown in Table 4.Cr and Ni were the major components of the slag heavy metal content while there was a small amount of Ba, Cu, Zn and Pb. No Cd, As and Hg was dete
22、cted.Steel slag may come in contact with rain water or leachate when it is used or processed. The dissoluble matters, such as metal ions and salts, m ay leach from the slag and migrate with the leachate, thus polluting the surrounding water body or soil.The leaching toxicity o f the slag can be eval
23、uated by the standard leaching test Table 5 lists the leaching concentrations of heavy metals by China standard leaching test( GB 5086. 2-1997) and the American standard (TCLP) .Compared with the corresponding limit values for the identification of hazardous waste, the leaching concentrations of hea
24、vy metals from stainless steel EAF slag are significantly lower (C r, Ni, Ba, Cu, Pb and Zn) or even undetectable (As, Cd, Hg and Cr).Though the content of Cr and Ni in EAF slag are relatively high( Tab le 4) , its leaching toxicity is low. The speciation distribution of five main heavy metal elements (Cr, Ni ,Ba, Zn and Cu) in EAF slag is shown in Fig. 3. It was observed that the majority of the heavy metals exist as residua ,organic matter-bound and iron /manganese oxide-bound fractions, which are relatively stable and hardly leach from slag. Only a small fraction is water
