Occurrence,leaching behavior,and detoxification of heavy metal Cr in coal gasification slag

Coal gasification slag(CGS)is a type of solid waste produced during coal gasification,in which heavy metals severely restrict its resource utilization.In this work,the mineral occurrence and distribution of typical heavy metal Cr in CGS is investigated.The leaching behavior of Cr under different conditions is studied in detail.Acid leaching-selective oxidation-coprecipitation method is proposed based on the characteristics of Cr in CGS.The detoxification of Cr in CGS is realized,and the detoxification mechanism is clarified.Results show that Cr is highly enriched in CGS.The speciation of Cr is mainly residual fraction(74.47%-86.12%),which is combined with amorphous aluminosilicate.Cr^(3+)and Cr^(6+)account for 90.93%-94.82%and 5.18%-9.07%of total Cr,respectively.High acid concentration and high liquid-solid ratio are beneficial to destroy the lattice structure of amorphous aluminosilicate,thus improving the leaching efficiency of Cr,which can reach 97.93%under the optimal conditions.Acid leaching-selective oxidation-coprecipitation method can realize the detoxification of Cr in CGS.Under the optimal conditions,the removal rates of Fe^(3+)and Cr^(3+)in the leaching solution are 80.99%-84.79%and 70.58%-71.69%,respectively,while the loss rate of Al^(3+)is only 1.10%-3.35%.Detoxification slag exists in the form of Fe-Cr coprecipitation(Fe_(1-x)Cr_xOOH),which can be used for smelting.The detoxification acid leaching solution can be used to prepare inorganic polymer composite coagulant poly-aluminum chloride(PAC).This study can provide theoretical and data guidance for detoxification of heavy metal Cr in CGS and achieve resource utilization of coal gasification solid waste.

Reconstruction and recovery of anatase TiO_(2) from spent selective catalytic reduction catalyst by Na OH hydrothermal method

The improper disposal of spent selective catalytic reduction (SCR) catalysts causes environmental pollution and metal resource waste.A novel process to recover anatase titanium dioxide (TiO_(2)) from spent SCR catalysts was proposed.The process included alkali (NaOH) hydrothermal treatment,sulfuric acid washing,and calcination.Anatase TiO_(2) in spent SCR catalyst was reconstructed by forming Na_(2)Ti_(2)O_(4)(OH)_(2) nanosheet during NaOH hydrothermal treatment and H_(2)Ti_(2)O_(4)(OH)_(2) during sulfuric acid washing.Anatase TiO_(2) was recovered by decomposing H_(2)Ti_(2)O_(4)(OH)_(2) during calcination.The surface pore properties of the recovered anatase TiO_(2) were adequately improved,and its specific surface area (SSA) and pore volume (PV) were 85 m^(2)·g^(-1)and 0.40 cm^(3)·g^(-1),respectively.The elements affecting catalytic abilities(arsenic and sodium) were also removed.The SCR catalyst was resynthesized using the recovered TiO_(2) as raw material,and its catalytic performance in NO selective reduction was comparable with that of commercial SCR catalyst.This study realized the sustainable recycling of anatase TiO_(2) from spent SCR catalyst.

Kinetics of the decomposition of dimethylhexane-1,6-dicarbamate to1,6-hexamethylene diisocyanate

The kinetics of the decomposition of dimethylhexane-1,6-dicarbamate to 1,6-hexamethylene diisocyanate was studied. A consecutive reaction model was established and the reaction orders for the two steps were confirmed to be 1 and 1.3 by the integral test method and the numerical differential method, respectively. The activation energies of the two steps were(56.94 ± 5.90) k J·mol-1and(72.07 ± 3.47) k J·mol-1with the frequency factors exp(12.53 ± 1.42) min-1and(14.254 ± 0.84) mol-0.33·L0.33·min-1, respectively. Based on the kinetic model obtained, the progress of the reaction can be calculated under given conditions.

Crystallization of calcium silicate at elevated temperatures in highly alkaline system of Na_2O–CaO–SiO_2–H_2O

In Na_2O–CaO–SiO_2–H_2O system,systematic investigations of phase and morphology of calcium silicate in hydrothermal conditions were concisely conducted for high-value utilization of silicon resource in high-alumina fly ash(HAFA).The results show that crystal composition and phase may be affected by relatively low concentration of NaOH,and sodium ions are rearranged into the structure to form NaCaHSiO_4 and Na_2Ca_3H_8Si_2O_(12) with different C/S ratio at high concentration of Na OH.In addition,phases in wollastonite group possess the morphology of nano fiber.Formation of nano fiber is attributed to the difference of surface energies between axial and radial direction,and higher temperatures lead to easier growth along radial direction.The preparation of C–S–H with different phases and morphologies can guide for the application of silicate solution with high alkalinity with different purposes.

干法电石渣杂质赋存及高效分离研究

电石渣中Ca(OH)_(2)含量达到了80%以上,针对电石渣中包含的大颗粒杂质影响其资源化利用的问题,采用了XRD,XRF, XPS, FTIR和化学分析等方法对杂质组分进行了系统分析,采用短程气固高效分离工艺对电石渣进行旋风分离,研究了旋风分离过程对杂质的分离效果和产品应用的影响。结果表明,电石渣中的碳主要以碳单质和碳酸盐形式存在,铝硅多以铝硅酸盐形式存在,硫主要以硫酸盐、硫化物和硫醇的形式存在;旋风分离后电石渣中粗颗粒显著富集,铁在粗渣中富集现象显著,铝硅和钙组分未富集,细渣中酸不溶物含量显著减少。利用电石渣制备活性氧化钙,旋风分离细渣所制备的氧化钙产品抗压强度达到了5.1 MPa,相对于原渣和旋风分离粗渣均提高了约50%;细渣制备的活性氧化钙产品中酸不溶物质量分数与原渣和粗渣相比也显著降低,为0.46wt%。本研究为电石渣的杂质分析及工业化应用提供了依据。

电石渣湿法脱硫过程亚硫酸钙强制氧化及杂质影响规律

电石渣主要成分为氢氧化钙,可以代替石灰石进行湿法烟气脱硫,但是电石渣的碱性较强,脱硫产物亚硫酸钙颗粒细小,可能会影响其氧化结晶过程。系统考察了不同工艺条件对亚硫酸钙氧化及硫酸钙结晶过程中粒径、氧化速度、含水率及微观形貌的影响规律,并得到优化的工艺条件:亚硫酸钙浓度为5 g/L,曝气量为400 mL/min,初始pH为5.5,反应温度为40℃,反应时间为4 h;在最优条件下得到了粒度大、含水率低、纯度高和形貌均匀的脱硫石膏(主要为二水硫酸钙)产品,有利于其后续的资源化利用。电石渣在酸性条件下各元素浸出的先后顺序为Na>Ca>Mg>Si>Fe>Al;在上述最佳反应条件下考察了Na,Mg,Si,Fe,Al等杂质对亚硫酸钙的氧化过程及硫酸钙结晶的影响,结果表明,Mg,Si,Fe对亚硫酸钙氧化速率有明显促进作用,而Al,Na抑制亚硫酸钙氧化;同时添加杂质Si对硫酸钙结晶几乎无影响,添加杂质Mg,Fe,Na对硫酸钙结晶影响较小,而添加杂质Al对硫酸钙结晶有明显不利影响。本研究以电石渣基亚硫酸钙为原料,开展了亚硫酸钙氧化与二水硫酸钙结晶研究,为工业实际电石渣脱硫的强制氧化过程提供理论指导。

Si/F/K/Na杂质对硫酸钙结晶过程的影响

考察了湿法磷酸生产过程中Si,F,K和Na等杂质对Ca SO4结晶过程的影响规律.结果表明,两种碱金属对Ca SO4结晶有不同作用,K有利于Ca SO4晶体生长,而Na含量增加则会抑制Ca SO4团聚;不同形式的K,Si和F对Ca SO4结晶的作用不同,Si O2对Ca SO4粒径影响不大,但会使其形貌不规则,H2Si F6会造成Ca SO4晶体分散,而K2Si F6有利于Ca SO4晶体生长.