影响红土镍矿回转窑直还原金属回收率的因素分析

回转窑直还原生产镍铁工艺是采用低品位红土镍矿生产镍铁的工艺,金属回收率的提高可明显降低生产成本。文章分别从原料情况、还原焙烧过程、选矿过程三个方面对回收率的影响因素做出具体分析,并提出了提高回收率的措施和办法。

新型煤基竖炉直接还原工艺的探讨

本文在外热式煤基竖炉的研究基础上，提出预热预还原段采用内热式对流传热和终还原段采用外热式传导传热相结台的煤基竖炉直接还原新工艺，并设计建造了模拟试验装置．试验表明，模拟试验装置具有操作方便、控制可靠的特点，同时取得了C／Fe比为0．5时，预还原时间为30min、终还原时间为100min，金属化率大于95％的良好指标．

Behaviors of vanadium and chromium in coal-based direct reduction of high-chromium vanadium-bearing titanomagnetite concentrates followed by magnetic separation

The reduction behaviors of FeO·V2O3 and FeO·Cr2O3 during coal-based direct reduction have a decisive impact on the efficient utilization of high-chromium vanadium-bearing titanomagnetite concentrates. The effects of molar ratio of C to Fe n(C)/n(Fe) and temperature on the behaviors of vanadium and chromium during direct reduction and magnetic separation were investigated. The reduced samples were characterized by X-ray diffraction(XRD), scanning election microscopy(SEM) and energy dispersive spectrometry(EDS) techniques. Experimental results indicate that the recoveries of vanadium and chromium rapidly increase from 10.0% and 9.6% to 45.3% and 74.3%, respectively, as the n(C)/n(Fe) increases from 0.8 to 1.4. At n(C)/n(Fe) of 0.8, the recoveries of vanadium and chromium are always lower than 10.0% in the whole temperature range of 1100-1250 °C. However, at n(C)/n(Fe) of 1.2, the recoveries of vanadium and chromium considerably increase from 17.8% and 33.8% to 42.4% and 76.0%, respectively, as the temperature increases from 1100 °C to 1250 °C. At n(C)/n(Fe) lower than 0.8, most of the FeO·V2O3 and FeO·Cr2O3 are not reduced to carbides because of the lack of carbonaceous reductants, and the temperature has little effect on the reduction behaviors of FeO·V2O3 and FeO·Cr2O3, resulting in very low recoveries of vanadium and chromium during magnetic separation. However, at higher n(C)/n(Fe), the reduction rates of FeO·V2O3 and FeO·Cr2O3 increase significatly because of the excess amount of carbonaceous reductants. Moreover, higher temperatures largely induce the reduction of FeO·V2O3 and FeO·Cr2O3 to carbides. The newly formed carbides are then dissolved in the γ(FCC) phase, and recovered accompanied with the metallic iron during magnetic separation.

Effect of calcium compounds on direct reduction and phosphorus removal of high-phosphorus iron ore

The increasing demand for iron ore in the world causes the continuous exhaustion of magnetite resources.The utilization of high-phosphorus iron ore becomes the focus.With calcium carbonate(CaCO_(3)),calcium chloride(CaCl_(2)),or calcium sulfate(CaSO_(4))as additive,the process of direct reduction and phosphorus removal of high-phosphorus iron ore(phosphorus mainly occurred in the form of Fe_(3)PO_(7) and apatite)was studied by using the technique of direct reductiongrinding-magnetic separation.The mechanism of calcium compounds to reduce phosphorus was investigated from thermodynamics,iron metallization degree,mineral composition and microstructure.Results showed that Fe_(3)PO_(7) was reduced to elemental phosphorus without calcium compounds.The iron-phosphorus alloy was generated by react of metallic iron and phosphorus,resulting in high phosphorus in reduced iron products.CaCO_(3) promoted the reduction of hematite and magnetite,and improved iron metallization degree,but inhibited the growth of metallic iron particles.CaCl_(2) strengthened the growth of iron particles.However,the recovery of iron was reduced due to the formation of volatile FeCl_(2).CaSO_(4) promoted the growth of iron particles,but the recovery of iron was drastically reduced due to the formation of non-magnetic FeS.CaCO_(3),CaCl_(2) or CaSO_(4) could react with Fe_(3)PO_(7) to form calcium phosphate(Ca_(3)(PO_(4))_(2)).With the addition of CaCO_(3),Ca_(3)(PO_(4))_(2) was closely combined with fine iron particles.It is difficult to separate iron and phosphorus by grinding and magnetic separation,resulting in the reduced iron product phosphorus content of 0.18%.In the presence of CaCl_(2) or CaSO_(4),the boundary between the generated Ca_(3)(PO_(4))_(2) and the metallic iron particles was obvious.Phosphorus was removed by grinding and magnetic separation,and the phosphorus content in the reduced iron product was less than 0.10%.

Methylenetetrahydrofolate reductase C677T genotype affects promoter methylation of tumor-specific genes in sporadic colorectal cancer through an interaction with folate/vitamin B_(12) status

AIM:To evaluate joint effects of Methylentetra-hydrofolate reductase(MTHFR) C677T genotypes,and serum folate/vitamin B12 concentrations on promoter methylation of tumor-associated genes among Iranian colorectal cancer patients. METHODS:We examined the associations between MTHFR C677T genotype,and promoter methylation of P16,hMLH1,and hMSH2 tumor-related genes among151 sporadic colorectal cancer patients. The promoter methylation of tumor-related genes was determined by methylation-specific PCR. Eighty six patients from whom fresh tumor samples were obtained and 81 controls were also examined for serum folate and vitamin B12 concentrations by a commercial radioimmunoassay kit. RESULTS:We found 29.1% of cases had tumors with at least one methylated gene promoter. In case-case comparison,we did not find a significant association between methylation in tumors and any single genotype. However,in comparison to controls with the CC genotype,an increased risk of tumor methylation was associated with the CT genotype(OR = 2.5;95% CI,1.1-5.6) . In case-case comparisons,folate/vitamin B12 levels were positively associated with tumor methylation. Adjusted odds ratios for tumor methylation in cases with high(above median) versus low(below median) serum folate/vitamin B12 levels were 4.9(95% CI,1.4-17.7) ,and 3.9(95% CI,1.1-13.9) ,respectively. The frequency of methylated tumors was significantly higher in high methyl donor than low methyl donor group,especially in those with MTHFR CT(P = 0.01) ,and CT/TT(P = 0.002) genotypes,but not in those with the CC genotype(P = 1.0) . CONCLUSION:We conclude that high concentrations of serum folate/vitamin B12 levels are associated with the risk of promoter methylation in tumor-specific genes,and this relationship is modified by MTHFR C677T genotypes.

Action rules of H_2 and CO in gas-based direct reduction of iron ore pellets

Alastraet： The gas-based direct reduction of iron ore pellets was carried out by simulating the typical gas composition in coal gasification process, Midrex and HyMII processes. The influences of gas composition and temperature on reduction were studied. Results show that the increasing of HE proportion is helpful to improve the reduction rate. However, when ~o（H2）：~o（CO）〉1.6：1, changes of HE content have little influence on it. Appropriate reduction temperature is about 950 ℃, and higher temperature （1 000 ℃） may unfavorably slow the reduction rate. From the kinetics analysis at 950 ℃, the most part of reduction course is likely controlled by interfacial chemical reaction mechanism and in the final stage controlled by a combined effect of gaseous diffusion and interfacial chemical reaction mechanisms. From the utilizations study of different reducing gases at 950 ℃, the key step in reduction course is the 3rd stage （FeO→Fe）, and the utilization of reducing gas increases with the rise of HE proportion.

Pilot scale test of producing nickel concentrate from low-grade saprolitic laterite by direct reduction-magnetic separation

The enrichment of Ni from a low-grade saprolitic laterite ore,which has been pre-treated by high pressure grinding roller（HPGR） to be 74% passing 0.074 mm and contains 0.92% Ni,18.47% Fe,10.61% MgO and 42.27% SiO2,was conducted by using pelletizing,rotary kiln reduction and magnetic separation process on a semi industrial scale,and the effects of reduction duration,mass ratio of coal to pellets（C/P）,the types of magnetic separator,the sections of grinding-separation and the grinding fineness on the recovery of Ni and Fe were examined.It is shown that nickel concentrate containing 3.13 % Ni and 59.20 % Fe was achieved at recoveries of 84.36 % and 71.51% for Ni and Fe,respectively under the following conditions：reducing at （1120±40） ℃ for 120 min,C/P being 1.0,wet grinding of reduced pellets up to 70%-87% passing 0.074 mm and a magnetic field intensity of 238.8 kA/m during the first section of grinding-magnetic separation,and a grinding fineness of 84%-91% passing 0.045 mm and a magnetic intensity of 39.8 kA/m during the second section of grinding-magnetic separation.The enriched Ni containing concentrate has a low content of S and P,and can be used for further processing to produce high-grade ferronickel alloy.

Synchronous enrichment of phosphorus and iron from a high-phosphorus oolitic hematite ore to prepare Fe-P alloy by direct reduction-magnetic separation process

In this study,direct reduction-magnetic separation process was applied to enrich phosphorus and iron to prepare Fe-P crude alloy from a high phosphorus oolitic hematite ore(HPOH).The results show that at lower temperatures and with absence of any of additives,Fe cannot be effectively recovered because of the oolitic structure is not destroyed.In contrast,under the conditions of 15%Na_(2)SO_(4)and reducing at 1050℃ for 120 min with a total C/Fe ratio(molar ratio)of 8.5,a final Fe-P alloy containing 92.40%Fe and 1.09%P can be obtained at an overall iron recovery of 95.43%and phosphorus recovery of 68.98%,respectively.This metallized Fe-P powder can be applied as the burden for production of weathering resistant steels.The developed process can provide an alternative for effective and green utilization of high phosphorus iron ore.

Preparing low-oxygen Ti-6Al-4V alloy powder through direct reduction of oxides and its synergistic reaction mechanism

Ti-6Al-4V alloy powder was prepared through a two-step reduction of a mixture of TiO_(2),V_(2)O_(5) and Al_(2)O_(3) in this study.The oxide mixture was first reduced by Mg in MgCl_(2) at 750℃ in argon,where oxygen was reduced to 2.47 wt%from 40.02 wt%.The oxygen content in the final powder was eventually reduced to an extremely low level(0.055 wt%)using calcium at 900℃ in argon,and the final powder had the composition of 90.12 wt%Ti,5.57 wt%Al,and 3.87 wt%V,which meets the standard specification of Ti-6Al-4V(ASTM F1108-09).Between the two reductions,a heat treatment step was designed to help controlling the specific surface area and particle size.The effect of the heat treatment temperature on the morphology,and composition uniformity of the powder was investigated in detail.Heat treatment above 1300℃ attributed to a dense powder with a controlled specific surface area.Thermodynamic modeling and experimental results indicated that onlyα-Ti enriched with Al andβ-Ti enriched with V exist in the final powder,and other possible phases including Al-Mg and Al-V were excluded.This study also offers a triple-step thermochemical process for producing high-purity Ti-based alloy powder.

Direct reduction of carburized pre-reduced pellets by microwave heating

A new iron-making process using carburized pre-reduced iron ore pellets and microwave heating is investigated. The pre-reduced pellets, with a porous structure, and fine particles are carburized homogeneously at 400-650 ℃ in a CO atmosphere. The carburized carbon not only acts reaction as a reduction agent, but also absorbs microwave in the reduction process. Hence, the carburized pre-reduced pellets can be rapidly reduced by microwave heating. There are three procedures involved in the process, namely, gas-based pre-reduction, low-temperatttre carburization and deep reduction by microwave heating. Carburized pre-reduced iron ore pellets show a rapid temperature rise that is twice as fast as the results for pre-reduced pellets in the laboratory. This not only improves the efficiency of the microwave heating, but also accelerates the reduction of iron oxides. The temperature of the pre-reduced pellets rises to 1050 ℃ in 45 min when the carburization rate is 2.02%, and the metallization rate and compressive strength reach 94.24% and 1725 N/pellet, respectively.

Sticking of iron ore pellets in direct reduction with hydrogen and carbon monoxide:Behavior and prevention

A series of reduction experiments of iron ore pellets with hydrogen,carbon monoxide and their mixture were carried out in a laboratory scale shaft furnace.The sticking behavior accompanying reduction of iron ore pellets was investigated.And morphology of the sticking interface forming during reduction was analyzed by SEM equipped with EDS.In order to evaluate the effects of the temperature and gas composition on sticking properties,reduction of iron ore pellets were conducted at 800-1000 ℃.The results show that the sticking strength of the pellets increases with temperature,however,decreases with hydrogen content in reducing gas.For an efficient shaft furnace operation in direct reduction(DR),relative prevention of sticking such as coating of pellets was also developed to solve sticking problem.The results show that CaO is a suitable material for the coating method.

Kinetics of carbothermic reduction of marmatite in presence of lime

The direct carbothermic reduction of marmatite in the presence of lime was studied by thermogravimetric method to determine the technical feasibility to produce Zn(g)without polluting with SO2(g).X-ray diffraction analysis of partially reacted samples indicated that the reduction occurred through the formation of ZnCaOS and Ca2Fe2O5 as intermediate products to yield Zn(g),and solid Fe and Ca S as the final products.Temperature had the major effect on the rate of reduction.Complete conversion of marmatite was obtained at 1100℃in about 10 min using 300 mg samples with molar ratio of(Zn,Fe)S:CaO:C equal to 1:1:1.The kinetics of the overall reduction reaction was analyzed by the model ln(1-X)=-kt,which represented the data well up to a fractional conversion of 0.95 in the temperature range of 1000-1150℃.The determined activation energy in this temperature range was 257 k J/mol.The results demonstrated the technical feasibility to produce Zn(g)by this method without producing noxious SO2(g)emissions.

Effect of reducing agents on reducing atmosphere in coal-based direct reduction of beach titanomagnetite

Beach titanomagnetite(TTM)provides a cheap alternative source of Fe and Ti,but this ore is difficult to process to make suitable concentrates for the blast furnace.Recently studies showed that it is feasible to separate Fe and Ti by coal-based direct reduction.In this study,beach TTM was selected as the research object,the effects of reducing agents on reducing atmosphere in coal-based direct reduction of beach TTM were analyzed,and the role of volatiles was also studied.The results showed that when bitumite and coke were used as reducing agents of TTM,the CO produced from volatiles was involved in the reduction reaction,and the generated CO_(2) provided the raw material for the reaction of TTM.The reduction effect of bitumite was better than that of coke.The reason is that bitumite+TTM had a higher gas generation rate and produced a higher CO partial pressure,while coke+TTM had a lower gas generation rate and produced a lower CO partial pressure.When graphite was used as a reducing agent,there was a solid-solid reaction in the early stage in the reaction.With the continuous accumulation of CO_(2),the Boudouad reaction started and accelerated.Graphite+TTM also produced a higher CO partial pressure.

A Fe-N-C catalyst with highly dispersed iron in carbon for oxygen reduction reaction and its application in direct methanol fuel cells

Exploring non‐precious metal catalysts for the oxygen reduction reaction （ORR） is essential for fuel cells and metal–air batteries. Herein, we report a Fe‐N‐C catalyst possessing a high specific surface area （1501 m2/g） and uniformly dispersed iron within a carbon matrix prepared via a two‐step pyrolysis process. The Fe‐N‐C catalyst exhibits excellent ORR activity in 0.1 mol/L NaOH electrolyte （onset potential, Eo=1.08 V and half wave potential, E1/2=0.88 V vs. reversible hydrogen electrode） and 0.1 mol/L HClO4 electrolyte （Eo=0.85 V and E1/2=0.75 V vs. reversible hydrogen electrode）. The direct methanol fuel cells employing Fe‐N‐C as the cathodic catalyst displayed promising per‐formance with a maximum power density of 33 mW/cm2 in alkaline media and 47 mW/cm2 in acidic media. The detailed investigation on the composition–structure–performance relationship by X‐ray diffraction, X‐ray photoelectron spectroscopy and Mo-ssbauer spectroscopy suggests that Fe‐N4, together with graphitic‐N and pyridinic‐N are the active ORR components. The promising direct methanol fuel cell performance displayed by the Fe‐N‐C catalyst is related to the intrinsic high catalytic activity, and critically for this application, to the high methanol tolerance.

Direct Reduction and Exact Solutions for Generalized Variable Coefficients 2D KdV Equation under Some Integrability Conditions

Based on the closed connections among the homogeneous balance （HB） method and Clarkson-KruSkal （CK） method, we study the similarity reductions of the generalized variable coefficients 2D KdV equation. In the meantime it is shown that this leads to a direct reduction in the form of ordinary differential equation under some integrability conditions between the variable coefficients. Two different cases have been discussed, the search for solutions of those ordinary differential equations yielded many exact travelling and solitonic wave solutions in the form of hyperbolic and trigonometric functions under some constraints between the variable coefficients.

Effects of minerals in ferric bauxite on sodium carbonate decomposition and volatilization

Direct reduction is an emerging technology for ferric bauxite utilization. However, because of sodium volatilization, its sodium carbonate consumption is considerably higher than that in ordinary bauxite processing technology. TG-DSC and XRD were applied to detecting phase transformation and mass loss in direct reduction to reveal the mechanism on sodium volatilization. The results show that the most significant influence factor of ferric bauxite on sodium volatilization in direct reduction system is its iron content. Sodium volatilization is probably ascribed to the instability of amorphous substances structure. Amorphous substances are the intermediate-products of the reaction, and the volatilization rate of sodium increases with its generating rate. These amorphous substances are volatile, thus, more sodium is volatilized with its generation. A small amount of amorphous substances are generated in the reaction between Na2CO3 and Al2O3; thus, only 3.15% of sodium is volatilized. Similarly, the volatilization rate is 1.87% in the reaction between Na2CO3 and SiO2. However, the volatilization rate reaches 7.64% in the reaction between Na2CO3 and Fe2O3 because of the generation of a large amount of amorphous substances.

Total plasma homocysteine and methylenetetrahydrofolate reductase C677T polymorphism in patients with colorectal carcinoma

AIM: To investigate the behaviour of total plasma homocysteine (tHcy) and its most common genetic determinant defect, the methylenetetrahydrofolate reductase C677T (C677TMTHFR) polymorphism in patients with early stage colorectal carcinoma. METHODS: tHcy was quantified by Abbott IMx immunoassay; screening for C677TMTHFR substitution was performed by PCR and restriction analysis. RESULTS: The frequency of the C/T and T/T genotypes of the C677TMTHFR gene polymorphism did not differ between the groups. The mean tHcy was statistically higher in cancer patients than in control subjects carrying the same C/C or C/T genotype, whereas there was no difference in the T/T homozygous carriers of the two groups. tHcy was significantly higher in the T/T homozygous carriers than in C/C and C/T genotype carriers. CONCLUSION: The statistically significant increase of tHcy observed in C/C and C/T genotype carriers among our cancer patients is related to substrate consumption dependent on the tumor cell proliferation rate, whereas the tHcy increase observed in T/T genotype carriers of both groups probably depends on the enzymatic deficit of the homocysteine conversion to methionine and/or on the folate deficiency.

Influence of furnace temperature and non-uniform heat flux density on direct reduction process of newly designed carbon containing pellet

In this study,innovative ellipsoid pellet with craters on its surface was designed,and the direct reduction process was compared with ellipsoid(without craters)and sphere pellets.In addition,furnace temperature and uneven heat flux density effects on the pellet direct reduction process were also studied.The results show that ellipsoid pellet is better than that of spherical pellet on metallization ratio.However,under the condition of non-uniform heat flow,the ellipsoid pellet final metallization rate and zinc removal rate were lower.Although the heat transfer effect of ellipsoid pellet with craters was not improved significantly,the metallization rate and zinc removal rate were found improved,which will have a cumulative effect on the pellets direct reduction process in rotary hearth furnace.Under varying furnace temperature conditions,the pellet temperature was higher than that of the constant furnace temperature.After 1200 s,pellet Fe concentration increased to 123.6%,metallization rate and zinc removal rate increased to 113.7%and 102.2%,respectively.These results can provide references for the carbon-containing pellet design used in rotary hearth furnace.

Swelling behavior of hot preheated pellets in reduction roasting process

One kind of facile coal-based direct reduction process is using hot preheated pellets for reduction in grate kiln. In this work, effects of reduction parameters on swelling index of hot preheated pellets were investigated by photographic technique under isothermal conditions. Experimental results show that swelling index of pellets is firstly increased then gradually decreased with increasing reduction time, while that is found to be an obvious decrease from 175 % to 30% with the variation of temperature from 900℃ to 1100℃. Results of XRD combined with SEM reveal that swelling behavior of pellets is decided by structure of newly formed metal iron grains. The formation and growth of fibers iron grains promote the increase in volume. Low temperature and low CO content are favored to the formation and orientated growth of metal iron grains in the one step process.

Thermodynamic analysis on the direct preparation of metallic vanadium from NaVO_3 by molten salt electrolysis

A novel and environmentally friendly route to directly prepare metallic vanadium from NaV03 by molten salt electrolysis is proposed. The feasibility about the direct electro-reduction of NaV03 to metallic vanadi- um is analyzed based on the thermodynamic calculations and experimental verifications. The theoretical decomposition voltage of NaV03 to metallic vanadium is only 0.47 V at 800 ℃ and much lower than that of the alkali and alkali earth metal chloride salts. The value is slightly higher than that of low-valence vanadium oxides such as V203, V305 and VO. However, the low-valence vanadium oxides can he further electro-reduced to metallic vanadium thermodynamically. The thermodynamic analysis is verified by the experimental results. The direct preparation of metallic vanadium from NaV03 by molten salt electrolysis is feasible.