不同作物原料热裂解生物质炭对溶液中Cd2+和Pb2+的吸附特性

选择由小麦秸秆、玉米秸秆和花生壳经350~500℃热裂解制成的生物质炭,研究生物黑炭对水溶液中Cd2+和Pb2+的吸附特性,分析了pH值、吸附时间、溶液初始质量浓度、生物质炭粒径和投加量对吸附效果的影响。结果表明:生物质炭对Cd2+和Pb2+的吸附约10 min即达平衡;3种生物质炭对Cd2+和Pb2+的等温吸附均可用Langmuir方程和Freundlich方程拟合,玉米秸秆炭对Cd2+和Pb2+的最大吸附量远大于小麦秸秆炭和花生壳炭;在生物黑炭投加量为150 mg(6 g.L-1)时,3种生物黑炭对溶液Cd2+的去除率均在90%以上,玉米秸秆炭对溶液Pb2+的去除率达90.30%,而小麦秸秆炭和花生壳炭的去除率仅为52%和47%,玉米秸秆炭有望成为处理重金属污染废水的新型吸附材料。     

人居生活废弃物生物黑炭对水溶液中Cd^2＋的吸附研究

以人居生活废弃物生物黑炭为材料,探讨生物黑炭对Cd^2＋的吸附动力学及热力学特性,通过平衡吸附法研究吸附时间、Cd^2＋初始质量浓度、吸附剂投加量、溶液pH值以及黑炭粒径对Cd^2＋吸附率的影响。结果表明,吸附时间为2h时基本达到吸附平衡,准二级动力学方程能很好地描述生物黑炭对Cd^2＋的吸附过程。Langmuir模型能较好地描述生物黑炭对Cd^2＋的等温吸附过程,根据该模型模拟得到25℃条件下Cd^2＋最大吸附量为6．22 mg·g^-1 Cd^2＋去除率随生物黑炭投加量的增加而增大;生物黑炭对Cd^2＋吸附量随其粒径减小而增大;溶液初始pH值为4．0-7．5时,pH值变化对Cd2’吸附量的影响不显著。采用人居生活废弃物生物黑炭去除水溶液中Cd^2＋时,控制溶液Cd^2＋初始质量浓度30mg·L^-1,粒径小于0．25mm,投加水平8g·L^-1,反应温度25℃,反应时间1-2h,Cd^2＋去除率可达80％。人居生活废弃物生物黑炭可以作为去除污染水体中Cd^2＋的吸附剂。     

人居生活废弃物生物黑炭对水溶液中Cd2+的吸附研究

以人居生活废弃物生物黑炭为材料,探讨生物黑炭对Cd2+的吸附动力学及热力学特性,通过平衡吸附法研究吸附时间、Cd2+初始质量浓度、吸附剂投加量、溶液pH值以及黑炭粒径对Cd2+吸附率的影响.结果表明,吸附时间为2h时基本达到吸附平衡,准二级动力学方程能很好地描述生物黑炭对Cd2+的吸附过程.Langmuir模型能较好地描述生物黑炭对Cd2+的等温吸附过程,根据该模型模拟得到25℃条件下Cd2+最大吸附量为6.22mg·g-1.Cd2+去除率随生物黑炭投加量的增加而增大;生物黑炭对Cd2+吸附量随其粒径减小而增大;溶液初始pH值为4.0～7.5时,pH值变化对Cd2+吸附量的影响不显著.采用人居生活废弃物生物黑炭去除水溶液中Cd2+时,控制溶液Cd2+初始质量浓度30mg·L-1,粒径小于0.25 mm,投加水平8g·L-1,反应温度25℃,反应时间1～2h,Cd2+去除率可达80％.人居生活废弃物生物黑炭可以作为去除污染水体中Cd2+的吸附剂.     

高锰酸钾改性活性炭的制备、表征及其吸附Pb2＋的特性

为提高活性炭对废水中Pb2＋的去除效率,采用不同浓度的KMnO4溶液对颗粒活性炭进行静置氧化/冷凝回流改性;利用BET测定了改性活性炭比表面积,并采用BET、SEM、FTIR和XRD等方法对其进行了表征;考察了吸附时间、投加量、pH值、温度对吸附Pb2＋的影响。结果表明,Pb2＋浓度为40 mg/L,在3 g/L的投加量下,0.01KMnO4-GAC和0.03KMnO4-GAC对Pb2＋的吸附去除率分别达到了92%和94%,是GAC对Pb2＋吸附去除率的1.84和1.88倍;在吸附剂3 g/L的投加量下,180 min基本达到吸附平衡;3种吸附剂对Pb2＋的吸附,随着pH值的降低而减少;而温度对吸附Pb2＋的影响相对较小。     

花生壳吸附Pb^2＋、Cu^2＋、Cr^3＋、Cd^2＋、Ni^2＋的动力学和热力学研究

以花生壳为生物吸附剂,通过序批式实验研究了吸附剂投量、吸附时间、金属离子初始质量浓度、吸附温度对吸附金属离子的影响,探讨了花生壳吸附的动力学及热力学特性。结果表明,准二级动力学方程能很好地描述花生壳对Pb^2＋、Cu^2＋、Cr^3＋、Cd^2＋、Ni^2＋的吸附过程。Langmuir模型和Freundlich模型均能较好地描述花生壳对5种重金属离子的等温吸附过程,而Langmuir模型拟合的线性更好。Pb2＋、Cu2＋、Cr3＋、Cd2＋、Ni2＋5种金属离子的最大吸附量分别是32.25、7.09、3.82、2.95、2.22 mg.g-1,花生壳可用于处理低质量浓度多种重金属混合的废水。热力学研究表明,花生壳对5种金属离子的吸附具有自发、吸热和熵增的特性。     

芦苇生物炭对水中铅的吸附特性

将芦苇秸秆在500℃下缺氧热解4 h制备成生物炭.采用批量平衡实验法,考察溶液p H值、生物炭投加量、溶液离子强度以及生物炭灰分对芦苇生物炭吸附水中Pb~(2+)的影响.结果表明:溶液p H值在2.0—5.5范围内,芦苇生物炭对Pb~(2+)的吸附量随着p H值升高而增加;生物炭最佳投加量为1.8 g·L-1,Pb~(2+)的去除率为96.6%;溶液中Na~+、Ca~(2+)的存在会抑制芦苇生物炭对Pb~(2+)的吸附;去除灰分后的生物炭对Pb~(2+)的吸附量降低.不同温度下的吸附等温线更符合Langmiur方程.在283、298、313 K下的最大实际吸附量分别为21.89、24.06、24.95 mg·g~(-1).热力学研究结果为ΔGθ0、ΔHθ0和ΔSθ0,说明该吸附是自发、熵增的吸热过程.吸附动力学线性拟合结果更符合假二级动力学方程.芦苇生物炭吸附前后的红外光谱和XRD衍射谱图分析表明吸附过程存在离子交换和阳离子-π作用.去除灰分的生物炭吸附Pb~(2+)后溶液中Na~+、K~+、Ca~(2+)、Mg~(2+)浓度升高,表明离子交换是主要吸附机制.     

农林废弃物基生物炭对重金属铅和镉的吸附特性

以沙柳、水稻和玉米秸秆3种农林废弃物为原材料,于500℃条件下热解制备生物炭,并通过元素分析、比表面积分析仪、扫描电镜(SEM)和红外光谱(FTIR)等分析方法对所制备的生物炭进行表征。探究了溶液初始pH、干扰离子强度和初始吸附剂投加量等因素对3种生物炭吸附Pb~(2+)和Cd~(2+)作用的影响,讨论了吸附动力学特性及吸附等温特性。结果表明:不同生物质制备出的3种生物炭的碱性和灰分含量由高到低依次为沙柳秸秆生物炭(SWB)、玉米秸秆生物炭(CB)和水稻秸秆生物炭(SB),FTIR检测结果显示3种生物炭表面均含有大量含氧官能团;当溶液pH为3～6时,3种生物炭对Pb~(2+)和Cd~(2+)吸附量随pH值的增加而升高,对Pb~(2+)的吸附效果随着溶液中离子强度的增强而降低,而SWB对Cd~(2+)的吸附效果随离子强度的增加而增加;3种生物炭对Pb~(2+)和Cd~(2+)的吸附过程符合准二级动力学模型,R~2均大于0.99,表明生物炭吸附速率主要由化学吸附机制决定;SWB、SB和CB对Cd~(2+)的吸附过程既符合Langmuir模型,又符合Freundlich模型,而生物炭对Pb~(2+)的吸附过程更适合Langmuir等温模型,表明生物炭对Pb~(2+)的吸附近似单分子层吸附,而对Cd~(2+)的吸附存在多分子层吸附。     

添加农作物秸秆炭对红壤吸附Cu(Ⅱ)的影响

为考察秸秆生物质炭在重金属污染红壤修复中的作用,用一次平衡法研究了由花生秸秆、大豆秸秆、稻草和油菜秸秆制备的4种生物质炭对采自江西和广西的2种红壤吸附Cu(Ⅱ)的影响及其机制。结果表明,添加由农作物秸秆制备的生物质炭提高了红壤对Cu(Ⅱ)的吸附量,生物质炭对Cu(Ⅱ)吸附的促进作用随生物质炭添加量的增加而增加,低pH值条件下促进作用更明显。pH值4.0和w为2%生物质炭添加水平下,油菜秸秆炭、花生秸秆炭、大豆秸秆炭和稻草炭使江西红壤对Cu(Ⅱ)的吸附量较对照分别增加97%、79%、51%和54%;花生秸秆炭和大豆秸秆炭使广西红壤对Cu(Ⅱ)的吸附量较对照分别增加61%和44%,当生物质炭添加水平w达4%时,Cu(Ⅱ)吸附量的增幅达97%和165%。生物质炭表面带负电荷,可以同时增加红壤对Cu(Ⅱ)的静电吸附量和专性吸附量,但以增加专性吸附为主。因此,添加秸秆生物质炭可以有效降低Cu(Ⅱ)在酸性红壤中的活动性和生物有效性。     

马铃薯秸秆生物炭对黄土吸附Cd(Ⅱ)的影响

为了探究来源于本地农业废弃物的生物炭对区域重金属污染黄土吸附固定化修复的可行性,本文采用批量平衡实验法,研究了马铃薯秸秆生物炭、黄土和生物炭与黄土混合物(加炭黄土)吸附重金属Cd(Ⅱ)的性能,考察了吸附时间、初始Cd(Ⅱ)浓度和溶液p H值对吸附过程的影响,并利用红外光谱、X-射线衍射分析等方法对吸附前后的生物炭和黄土分别进行表征.结果表明,生物炭、黄土、加炭黄土对Cd(Ⅱ)的吸附等温模式符合Langmuir模型,在25℃下的最大吸附量分别为15.60、7.87、12.40 mg·g~(-10,吸附动力学数据满足准二级动力学方程,溶液初始p H值对Cd(Ⅱ)的吸附过程影响较大,2p H4和6p H8时,吸附量增加速率很快,而4p H6时,吸附量平缓上升.表征结果说明离子交换和阳离子-π作用为生物炭对Cd(Ⅱ)的主要吸附机制,而黄土对Cd(Ⅱ)的吸附主要归因于石英、高岭石等黏土矿物以及有机质中的羧基基团.对比动力学和等温吸附数据可得,在实验研究范围内,生物炭的添加使黄土对Cd(Ⅱ)的吸附能力分别提高了41.50%和49.94%.因此,在一定条件下,生物炭的输入可有效提高黄土对Cd(Ⅱ)的吸附固定化能力.     

富磷污泥生物炭去除水中Pb(Ⅱ)的特性研究

以城市污水厂富磷剩余污泥为研究对象,考察高温热解制备生物炭吸附剂对水中Pb(Ⅱ)的去除效果.研究表明,随着热解温度升高,制备的生物炭对Pb(Ⅱ)的吸附能力增强;在相同热解温度下,生污泥生物炭对Pb(Ⅱ)的吸附能力比消化污泥生物炭大.采用700℃热解1 h制备生污泥生物炭以研究对Pb(Ⅱ)吸附的影响因素,结果显示:吸附180 min达到吸附平衡;富磷污泥生物炭对Pb(Ⅱ)的去除率随pH增加而升高;生物炭投加量增加,对Pb(Ⅱ)去除率上升,而单位吸附容量迅速减小.污泥生物炭对Pb(Ⅱ)的吸附符合准二级反应动力学,Langmuir模型比Freundlich模型能更好地拟合等温吸附线.在pH 5.0、吸附时间3 h、生物炭投加量20 g.L-1条件下,对Pb(Ⅱ)的最大吸附量为34.5 mg.g-1,表明富磷污泥生物炭可以作为一种廉价的吸附剂.     

硅藻土和膨润土对重金属离子Zn~（2＋）、Pb~（2＋）及Cd~（2＋）的吸附特性

以硅藻土和膨润土作为吸附剂,考察微波加热与否条件下,不同吸附时间、不同吸附剂用量和不同pH值对硅藻土和膨润土分别吸附Zn2＋、Pb2＋、Cd2＋重金属离子的影响.实验结果表明,硅藻土和膨润土对3种重金属离子均有很好的吸附效果,吸附时间对去除率影响不大,数分钟即可达到吸附平衡,微波加热、增加吸附剂用量和提高pH值,都有利于提高3种重金属离子的去除率.     

Recovery of NH 4 + by corn cob produced biochars and its potential application as soil conditioner

NH4^＋ ion, a main pollutant in aquatic systems, not only causes eutrophication in rivers and lakes but also contributes to fish toxicity. In this study, an eco-friendly biosorbent was prepared from the pyrolysis of corn cob, a low-cost agricultural residue. The biochars produced by pyrolysis of corn cob at 400℃ and 600℃ were characterized and investigated as adsorbents for NH4＋ -N from an aqueous solution. The biochars were characterized through elemental analysis, Brunauer-Emmett-Teller-N2 surface area analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy. Batch experiments were conducted to investigate the NH4＋ adsorption process of the corn cob biochars. The Freundlich isotherm model fitted the adsorption process better than the Langmuir and Dubinin-Radushkevich isotherm models. Moreover, the adsorption process was well described by a pseudo-second-order kinetic model. Results of thermodynamic analysis suggested that adsorption was a nonspontaneous exothermic process. Biochars produced at 400℃ had higher adsorption capacity than those produced at 600℃ because of the presence of polar functional groups with higher acidity. The exhausted biochar can be potentially used as soil conditioner, which can provide 6.37 kg NH4＋-N-t^-1 （N fertilizer per ton of biochar）.     

Performance and mechanism for cadmium and lead adsorption from water and soil by corn straw biochar

Cadmium (Cd) and lead (Pb) in water and soil could be adsorbed by biochar produced from corn straw. Biochar pyrolyzed under 400°C for 2 h could reach the ideal removal efficiencies (99.24%and 98.62% for Cd and Pb, respectively) from water with the biochar dosage of 20 g·L^–1 and initial concentration of 20 mg·L^–1. The pH value of 4–7 was the optimal range for adsorption reaction. The adsorption mechanism was discussed on the basis of a range of characterizations, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Raman analysis; it was concluded as surface complexation with active sorption sites (-OH, -COO-), coordination with π electrons (C = C, C = O) and precipitation with inorganic anions (OH^-, CO₃ ^2–, SO₄ ^2–) for both Cd and Pb. The sorption isotherms fit Langmuir model better than Freundlich model, and the saturated sorption capacities for Cd and Pb were 38.91 mg·g^-1 and 28.99 mg·g^–1, respectively. When mixed with soil, biochar could effectively increase alkalinity and reduce bioavailability of heavy metals. Thus, biochar derived from corn straw would be a green material for both removal of heavy metals and amelioration of soil.

Open image in new window

     

Lead(II) and cadmium(II) removal from aqueous solution using processed walnut shell: kinetic and equilibrium study

The biosorption potential of processed walnut shell for Pb(II) and Cd(II) ions from aqueous solutions was explored. The effects of pH, contact time, initial ion concentration, and amount of dried adsorbent were studied in batch experiments. The maximum adsorption was achieved within the pH range 4.0–6.0. The equilibrium data were well fitted by the Langmuir isotherm model. The maximum monolayer adsorption capacities were found to be 32?g?kg^?1 and 11.6?g?kg^?1 for Pb(II) and Cd(II) ions, respectively. Kinetic data were best described by the pseudo-second-order model. The structural features of the adsorbent were characterized by Fourier transform infrared spectroscopy, which confirmed the involvement of hydroxyl (–OH), carboxyl (–COO^–), and carbonyl (C=O) groups in metal sorption. This readily available adsorbent is efficient in the uptake of Pb(II) and Cd(II) ions from an aqueous solution and could be used for the treatment of wastewater streams bearing these metal ions.