风化煤源腐殖质和热活化牡蛎壳修复镉、砷复合污染土壤的机制和技术研究

农田重金属污染面广量大，常呈镉、砷复合污染，治理修复的难度很大；重金属污染场地通常浓度较高、毒性大，缺少经济有效的治理技术。面对这些挑战，有必要研发高效、安全、低成本的修复材料和使用技术。本研究以数量大、来源广的风化煤和牡蛎壳为原料，经碱液提取和加热改性获得了难溶性腐殖质、活化牡蛎壳钝化剂以及水溶性腐殖质淋洗剂，采用红外光谱、扫描电镜、X-射线衍射等分析方法对其进行理化性质的表征，结合批平衡试验和动力学模型分析钝化剂和淋洗剂与镉和砷的结合过程和机制，对不同类型（红壤、黑土、潮土）的Cd、As复合污染土壤进行分级提取、批淋洗试验及盆栽试验，探究钝化剂和淋洗剂对于Cd和As的结合形态、生物有效性的影响。主要研究结果如下： （1）从风化煤提取的腐殖质具有良好的化学性质。用0.1 M的KOH溶液以液:固比40:1对新疆风化煤进行一次性提取获得的腐殖质淋洗剂具有较高的芳香性和丰富的含氧官能团。其羧基和酚羟基含量分别是7.55和2.84 mol/kg。此外，影响淋洗剂修复效果的重要参数临界胶束浓度（CMC）比同类商品腐殖质淋洗剂低，因而性能更好。 （2）煅烧可以改变牡蛎壳的理化性质。煅烧导致了牡蛎壳的pH升高、比表面积呈现先升后降的波动变化，这与牡蛎壳的表面形貌由加热前的碳酸钙-蛋白质片层结构和不规则微孔转变为矩形块状结构的微米级CaO颗粒有关。XRD和FTIR图谱验证了牡蛎壳中的矿物成分由CaCO3到CaO的转化。 （3）腐殖质淋洗剂对红壤、黑土、潮土中的Cd和As均有良好的去除效果，在pH接近中性时更利于土壤中Cd的洗脱。腐殖质淋洗剂在pH = 7、浓度为3672 mg C/L、液:土比为30:1、单次洗涤6~12 h的条件下，可去除红壤中41.9 mg Cd/kg和199.3 mg As/kg，黑土中33.5 mg Cd/kg和291.5 mg As/kg，潮土中30.4 mg Cd/kg和325.5 mg As/kg。土壤中Cd、As的去除机制包括Cd与腐殖质的外、内环络合、腐殖质-阳离子-As的键合以及As与腐殖质酚羟基的结合。800 ℃煅烧活化的牡蛎壳（OS800）可以作为洗脱废液的处理剂，同时去除Cd、As和有机质（TOC）。 （4）OS800和难溶性腐殖质对土壤中Cd、As具有良好的钝化效果。以2.0%的添加量施入Cd、As复合污染农田土壤后，OS800可使土壤中交换性Cd从60%降低至27%。在小白菜盆栽试验中，当添加量为2.0%时，OS800可使小白菜可食部分的Cd含量降低了98%，As降低了73%；难溶性腐殖质使可食部分的Cd含量降低了98%，As降低了71%，均符合国家食品安全标准。 （5）两种钝化剂修复土壤后，Cd、As的胃、肠阶段的可给性均降低。修复后土壤中Cd的胃阶段可给性为62.45~80.66%、肠阶段可给性为22.92~52.06%；As的胃阶段可给性为27.89~46.52%、肠阶段可给性为22.10~54.32%。相反，修复前土壤Cd、As的胃肠液提取态含量均超过添加OS800或难溶性腐殖质后的含量，说明钝化剂的添加显著降低了土壤中经口摄入的Cd、As对人体产生危害的风险

Processes of Leonardite Altering Cation and Anion Composition of Soil Solution in Salt-affected Soil in the Yellow River Delta

【Objective 】To ameliorate salt-affected soil in the Yellow River Delta for productive use is of great social and economic significance to the region. Trials have been conducted to use leonardite as a soil amendment for the purpose, but failed to get consistent results and probe in-depth into the causes. This research aimed to assess changes in salt composition of the soil solution in the salt-affected soil applied with leonardite, and reveal processes and mechanisms of the changes.【Method 】Three topsoil samples(S1, S2 and S3), different in salt contents(1.0,7.5, and 35.3 mg·g~(-1), respectively), were collected from a farmland in the Yellow River Delta. After being air dried and gently ground to pass a 100-mesh sieve, the samples were mixed, separately, with leonardite at 0%,1%, 3%, and 5% in dosage and each treatment had two replicates. Then the mixtures were prepared separately into suspensions(solid: water = lg: 5 ml), which were shaken at 300 r·min~(-1) for 7 d and then centrifuged at 3 000 r·min~(-1) for 10 min. The obtained supernatants(or soil extracts) went through a 0.45-µm filter and got ready for analysis of Ca~(2+), Mg~(2+), K+, Na~+, Cl~-, NO_3~-, and SO_4~(2-) with ion chromatography. The leonardite used in the experiment was digested by HNO_3-HCIO_4-HF for analysis of Ca~(2+), Mg~(2+), K~+,and Na~+, and its carboxyl and phenolic hydroxyl groups were determined with the titration method of the International Humic Substances Society.【Result 】The leonardite was found to contain Na~+(1.66 mg·g~(-1)), K~+ (1.07 mg·g~(-1)), Ca~(2+)(19.97 mg·g~(-1)), Mg~(2+)( 1.60 mg·g~(-1)),carboxyl group(2.74 mol·kg~(-1)) and phenolic hydroxyl group(1.63 mol·kg~(-1)). In the soil solution, sodium adsorption ratio(SAR) decreased with leonardite increasing in spiking dosage, which was attributed to Ca~(2+) release from and Na~+ adsorption to leonardite. In the treatment of adding 5% leonardite to soil S2 SAR reduced from 7.81 to 6.61. In analogy to SAR, Cl~-/SO_4~(2-) molar ratio was proposed as a new indicator to reflect changes in anion compositions. It decreased from 10.20 to 8.25 in the treatment, which was a result of SO_4~(2-) release from and/or Cl~- retention by leonardite. The reduction of SAR and Cl~-/SO_4~(2-) ratio suggests that leonardite could lessen the toxic effects of Na~+ and Cl~- on plants.【Conclusion 】With Ca~(2+) and abundant carboxyl groups it contains, leonardite could alter ion compositions in soil solution via: 1) ion exchange between Ca~(2+) in leonardite and Na~+ in soil solution, reducing Na~+ concentration in the solution and its harmful effect; 2) replacement of Na~+ adsorbed on soil colloids by Ca~(2+) released from leonardite, favoring formation of soil aggregates and leaching of Na~+; and 3 ) formation of complexes of Na~+ in solution with organic substances dissolved from leonardite, reducing Na~+ activity and toxicity. It is, therefore, proposed that SAR and Cl~-/SO_4~(2-) ratio be tested as indicators for fast laboratory assessment of suitability of soil amendments for use in salt-affected soils, which would help land managers choose proper soil amendments for use and avoid input of Na-rich organic materials, such as sodium humate, in salt affected soils

Equipment and technology of field preparation of biochars from agricultural and forest residues under aerobic conditions with water-fire coupled method

Biochar has been reported for its beneficial effects on soil carbon sequestration, soil fertility improvement, and the immobilization of metal and organic contaminants in soils. Its large-scale agricultural and environmental application, however, is constrained by its high production cost in association with expensive equipment and operations and its high transportation cost of moving agricultural and forest residues to biochar production plant and delivering biochar to the end users. Exploring a technology for directed conversion from agricultural and forest residues to biochar in the field for local applications can significantly reduce the production and transportation costs of biochar, thus helping its applications. By mimicking the nature, where only agricultural and forest residues, water and fire were required for biomass carbonization and charcoal formation, a method for biochar production in the field was proposed and described in details. Briefly, this involved an aerobic process of biomass carbonization in a brick-constructed trough, and the formation of biochar by a fire-water coupled method. The carbonization process had the dual features: combustion on the surface of biomass and oxygen-limiting pyrolysis inside of the biomass. Three operational processes of aerobic carbonization and its termination were used to suit the production of biochars from different types of residues: 1) Large Salicaceae branches were ignited at one direction of the trough for aerobic carbonization, followed by a water-mist spray for immediate termination of the carbonization; 2) Medium-size cotton stalk was ignited at one direction for carbonization and then sprayed by a water column to crosscut formed biochar; 3) Small hollow reed straw was ignited at multiple directions, then water mist was sprayed layer by layer on biomass. The dislocated holes on side walls of brick trough performed as ignition points, channels for water mist and air ventilation channels. The biochars produced in the field by the proposed technology were characterized in this study. The biochars were relatively homogeneous, and the conversion rates from biomass to biochar were about 30%. Carbon content of biochar was 43.49%-60.30%, and nitrogen content was 0.52%-0.86%. The biochar also contained the abundant surface functional groups, with a carboxyl group content of 0.98-1.09 mol/kg and a phenolic hydroxyl group content of 0.53-0.59 mol/kg, and the specific surface area of the biochars varied between 16.0 and 262.2 m~2/g, which underpins their use as adsorbents for cations, such as ammonium ions and some heavy metals and other extraneous ions and molecules. The flue gas generated from the burning of the Salicaceae, cotton stalk, and reed straw in the carbonization process was treated by a multiple-step process to reduce particulate matter concentrations. PM 2.5 in the treated flue gas was reduced to 56, 66 and 68 mug/m~3 for Salicaceae, cotton stalk, and reed straw, respectively, and the corresponding PM 10 was reduced to 100, 114 and 128 mug/m~3, which meet the national emission standard. The biochar preparation technology provided herein is simple to operate, low in cost, and highly efficient. Based on labor, fuel, and water inputs, the productivity was 1 t/d per person, and the cost was 162.5 yuan/t by farmers. This technology for producing low-cost biochar would make its agricultural and environmental applications feasible.</p

Biomass feedstocks and carbonization methods affect antibiotic adsorption on biochar

Biochar has been reported as a useful adsorbent of organic contaminants. Here, reed, cotton stalk, and bamboo willow were selected as feedstocks to produce biochars via oxygen-limited or aerobic methods for carbonization. The obtained biochars were first characterized for their physical and chemical properties and then investigated for their performance in adsorbing oxytetracycline（OTC） and sulfamethoxazole（SMX）. It was found that both feedstocks and carbonization methods affected OTC and SMX adsorption. Reed and cotton stalks were better carbonized under oxygen-limited conditions to produce biochars（O2-limited biochars）, whereas bamboo willow was suitable to produce biochars via aerobic carbonization（aerobic biochar）. The aerobic biochar adsorbed 11.98 and 10.12 mg/g of OTC and SMX, respectively, from a solution with an initial concentration of 50 mg/L of the biotics. Batch adsorption experiments and the Fourier transform infrared spectroscopic analysis indicated that π-π electron donor-acceptor interaction was the primary mechanisms for OTC and SMX adsorption on the aerobic biochar. Electrostatic attraction further promoted OTC adsorption on aerobic biochar at high pHs, whereas pore filling could contribute to SMX adsorption. This work showed that aerobic biochar were better adsorbents of OTC and SMX than O2-limited biochars, and suggested that biochar adsorbents can be tailor-made for different contaminants by judicious selection of feedstocks and carbonization processes

Humic nanoparticles for remediation of Cd- contaminated soils

Extraneous humic substances could alter the dynamics of Cd in soils. An insoluble humic acid, produced from a leonardite, was used in laboratory experiment as an adsorbent to immobilize Cd in a silt-loam soil near a smelting plant and a Cd-spiked and aged sandy-loam soil, whereas a soluble peat-derived potassium humate was employed as a washing agent to mobilize Cd in, and remove it out of, the contaminated soils. Addition of 2% humic acid could reduce CaCl_2 extractable Cd in a soil (0.103 mg·L~(-1)) by 19.7%. This immobilization effect was greater in sandy-loam soil than in silt-loam soil. Similarly, Cd removed from the contaminated soils increased with washing agent dosage. A single washing at 10 g·L~(-1) of potassium humate removed up to 38.1% of the total Cd in soils. Fourier transform infrared spectroscopic analysis indicated the formation of Cd-carboxyl complex. This study suggests that Cd-contaminated soils can be remediated by humic substances through either an immobilization or mobilization process. The key to the success is to select humic substances with a suitable solubility: water insoluble humic acid for Cd immobilization and water soluble potassium humate for effective removal of Cd out of soils

Humic acid from leonardite for cadmium adsorption and potential applications

以碱溶酸析＂法从新疆风化煤中提取的胡敏酸为研究对象,对其理化性质和表面形态进行表征,并通过吸附试验探究反应时间、溶液pH、镉离子（Cd（2＋））质量浓度对胡敏酸吸附Cd（2＋）的影响.结果表明：风化煤提取的胡敏酸碳元素质量分数高达58.68%,羧基的质量摩尔浓度为5.81mol/kg,等电点为2.7;该胡敏酸含Cd量为0.15mg/kg,符合国家土壤环境质量标准.胡敏酸对Cd（2＋）的吸附在8h内达到平衡,吸附量随Cd（2＋）质量浓度（0～100mg/L）和溶液pH升高而增加,到pH=6.0时最大,之后胡敏酸开始溶解导致吸附量降低.Langmuir方程比Freundlich方程能更好地拟合胡敏酸对Cd（2＋）的吸附等温线,显示出单分子层吸附的特点.在pH=5.0时,胡敏酸对Cd（2＋）的饱和吸附量达137.37mg/g,相当于用去了酸度系数（pKa）为3的羧基含量的71%.在pH=4.3、Cd（2＋）初始质量浓度为80mg/L的同等条件下,新疆风化煤提取的胡敏酸对Cd（2＋）的吸附量为86.97mg/g,高于国际腐殖质协会胡敏酸标样1R106H对Cd（2＋）的吸附量（73.49mg/g）.风化煤来源广、储量大、价格低,以它为原料制备获得的胡敏酸产量高、吸附能力强、环境友好、施用安全,有望作为吸附剂用于含重金属废水处理,以及作为钝化剂和土壤调理剂用于重金属污染土壤的修复

Biochars Made in the Field Using Coupled Oxygen-Limiting and Mist-Spraying Technique and Their Properties

Biochars have a range of functions from improving soil properties and remediating contaminated soils to reducing greenhouse gas emission from soil and increasing carbon content in soil.Their large-scale application,however,has been constrained by high costs of production and transportation.To solve this problem,a novel method has been developed for biochar production in the field with a coupled oxygen-limiting and mist-spraying technique.Agricultural and forest residues are placed in a soil trough and compacted layer by layer,a steel square tube with multiple holes is imbedded in the biomass,and an iron mesh is put on the top of it.The tube has the function of adjusting ventilation and oxygen supply to maintain flame temperature during biomass burning;and the mesh allows for the formation of a water film to limit oxygen supply.In field operations,cotton stalk or Salicaceae in the trough is ignited at one direction,whereas reed straw is ignited at multiple positions,for biomass carbonization,followed by water mist spraying layer by layer for a quick stop of carbonization.The biochars thus obtained have a yield of about 30%and are relatively homogeneous.They have abundant carboxyl group (0.71-1.43 mol/kg)and phenolic hydroxyl group(0.43-1.09 mol/kg)and a specific surface area of 45.5-83.2 m~2/g.Being able to produce goodquality biochars directly in the field at a low cost,this method makes feasible agricultural and environmental application of biochars.</p

一种用于重金属钝化的土壤调理剂及其制备方法

本发明涉及一种用于重金属钝化的土壤调理剂及其制备方法。该制备方法为：由富含腐殖酸的物料和强碱溶液混合，加热后提取的腐殖酸经联合絮凝方法得到用于重金属钝化的土壤调理剂。本发明利用分布广泛、储量丰富、廉价易得的褐煤和风化煤为原料，经环境友好过程提取，用首创的联合絮凝法制得用于重金属钝化的土壤调理剂。本发明的土壤调理剂由腐殖酸钙组成，富含羧基、羟基等功能基团，能有效吸附重金属，从而降低它们的生物有效性，可用于包括酸性土壤在内的重金属污染农田的调理和修复

Humic acid from leonardite for cadmium adsorption and potential applications

以碱溶酸析"法从新疆风化煤中提取的胡敏酸为研究对象,对其理化性质和表面形态进行表征,并通过吸附试验探究反应时间、溶液pH、镉离子(Cd~(2+))质量浓度对胡敏酸吸附Cd~(2+)的影响.结果表明:风化煤提取的胡敏酸碳元素质量分数高达58.68%,羧基的质量摩尔浓度为5.81mol/kg,等电点为2.7;该胡敏酸含Cd量为0.15mg/kg,符合国家土壤环境质量标准.胡敏酸对Cd~(2+)的吸附在8h内达到平衡,吸附量随Cd~(2+)质量浓度(0~100mg/L)和溶液pH升高而增加,到pH=6.0时最大,之后胡敏酸开始溶解导致吸附量降低.Langmuir方程比Freundlich方程能更好..