Study On The Preparation Of Mineral Admixtures By The Nickel Residue Produced During The RKEF Nickel-iron Or Stainless Steel Smelting Process

Several kinds of nickel slags are produced during the RKEF nickel-iron or stainless steel smelting process of lateral nickel ore.In order to solve the problem of environmental pollution that caused by the accumulation of nickel slag in Yangjiang?Guangdong Province?and alleviate the shortage of mineral admixtures in the Guangdong-Hong Kong-Macao Greater Bay Area,this paper investigated the preparation of mineral admixture by synergistic utilizing nickel-iron blast furnace slag?NBFS?,nickel-iron electric furnace slag?NEFS?,and nickel-iron refining slag?NRS?,which produced by the RKEF nickel-iron or stainless steel smelting process.Firstly,in this paper,the chemical and mineral composition of the three kinds of nickel slags and the safety feasibility as mineral admixture were studied.The results showed that the main chemical composition of NBFS was,Si O2,Ca O and Mg O;the main phase was amorphous,and the main crystal phase was spinel crystal.the main chemical composition of NEFS was Si O2 and Mg O,and the content ofand Ca O was low;the main phase was crystal phase,and the main crystal phase was forsterite crystal.the main chemical composition of NRS was Ca O,Si O2,Mg O and;the main phase was crystal phase,and the main crystal phase was?-C2S,diopside,magnesite,magnesia pyroxene and perovskite crystals.When NBFS and NEFS powders were used as building materials,they had no influence on the structural safety and environmental safety of the applied products.The autoclave soundness of NRS powder was unqualified,and the leaching toxicity of Cr⁶⁺did not meet the requirements of the first-class surface water standards.Therefore,when NRS powder was used as building materials,it had an adverse effect on the structural and environmental safety of the applied products.Next,the performance and mechanism of the three kinds of nickel slags used as mineral admixture were studied.The grinding characteristics of three kinds nickel slags and the grinding enhancement effect of different types of grinding aids on the nickel slags were also studied to lay the foundation for determining the production technology route of composite mineral admixture.The results showed that,when the specific surface area was around 450m²/kg,the fluidity ratio of mortar with admixture of the three kinds of nickel slags was as following:NEFS>NBFS>NRS;the compressive strength of mortar with admixture of the three kinds of nickel slags was as following:NBFS>NEFS>NRS.When NBFS powder was used as mineral admixture,it could meet the related requirements in industry standard JC/T 2503 as G100;when the specific surface area was 521m²/kg,NEFS powder could meet the related requirement in industry standard JC/T 2503 as D70;the performance of NRS was the worst and failed to meet the standard requirements when used as mineral admixture.When the specific surface area was around 450 m²/kg,the grindability of the three kinds of nickel slags was as following:NRS>NEFS>NBFS.When the grinding time was 45 minutes,the grinding effect and strengthening effect of ethyl acetate on NBFS was the best,and the optimal dosage is 0.01%.The grinding effect and strengthening effect of sodium sulfate on NEFS was the best,and the prepared NEFS powder could meet the related requirements in industry standard JC/T 2503 as D80 when blended with 0.3%sodium sulfate.The grinding effect and strengthening effect of TEA on NRS was the best,and optimal dosage is 0.03%;sodium sulfate could increase the specific surface area of NRS and act as an activator,and the prepared NRS powder could meet the related requirements in industry standard JG/T 486 as ordinary type III composite mineral admixture when blended with 0.2%or 0.3%sodium sulfate.The hydration characteristics of the three kinds of cement-nickel slags powder cementitious material was studied by analyzing the hydration heat in 0-7 d,the amount of calcium hydroxide and chemically combined water volume at the age of 7 d and 28 d,and the pore structure of hardened paste at the age of 28 d.The results showed that,during the period of 0 d-3 d,the hydration reaction rate of the three kinds of nickel slags powder was as following:NRS>NBFS>NEFS.During the period of 3 d-7 d,NBFS and NEFS continued to hydrate,and the active ingredients in the NRS were reacted completely;the hydration degree of NBFS was higher than that of NRS,and the hydration degree of NEFS was equal to or even higher than that of the NRS.During the period of 7 d-28 d,NBFS continued to hydrate and the speed of reaction become faster,which made the hydration degree catch up with or even higher than that of cement paste;the rate of hydration degree of NEFS was low,and NRS almost no longer reacted.Therefore,the mechanism of three kinds of nickel slags as mineral admixture was obtained:NBFS powder mainly produced pozzolanic reaction in composite cementitious materials,and the secondary hydration reaction continued,which made the compressive strength of mortar increase rapidly.NRS had high reactivity during the period of 0 d?3 d,and then the strength growth was small,which mainly produced filling effect;the compressive strength of mortar was low at 7 days and 28 days.The reactivity of NEFS was weakest at the1d and 3d,its reactivity at 7d and 28d is higher than that of NRS due to the pozzolanic effect.Furthermore,the effects of mix proportion and grinding method of admixtures produced by using three kinds of nickel slags powder on the properties were studied,which provided a reference for the production of different grades composite mineral admixtures that meet the requirements of the standard.The results showed that,the optimum performance was obtained when the mix proportion was 4:3:3 for NRS:NEFS:NBFS.And the flow rate,7 d and 28 d activity index of the mortar with the optimum performance was 103%,81%and 88%,respectively,which meet the related requirements in industry standard JG/T486 as type II compound admixture.The cascade-grinding was suitable for the preparation of composite mineral admixtures by using the three kinds of nickel slags,which can greatly exert the"pozzolanic effect"of high activity ingredients and the"filling effect"of low activity ingredients.During the cascade-grinding process,high activity particles with poor grindability could be used as the"grinding medium",which could have grinding effect and reduce energy consumption.When the primary grinding time was 35min,the secondary grinding time was25min,and the effective grinding time?Q?=35.5min,the composite mineral admixture prepared by the cascade-grinding method had the best performance,and the flow rate,7 d and28 d activity index of mortar prepared with the admixture was 105%,93%and 92%respectively,which meet the related requirements in industry standard JG/T486 as type?compound admixture.Finally,the results of this paper helped Yangjiang Dadi Environmental Protection Building Material Co.,Ltd.in Guangdong Province successfully build a composite mineral admixture production line with stable production.The study is of great significance to the sustainable development of the nickel-iron stainless steel industry and local environmental protection.Meanwhile,the resource utilization of nickel slag can also produce huge economic and social benefits.