秸秆-磷石膏联用对赤泥的腐殖质组分和微生物群落的影响

腐殖化过程是赤泥土壤化及堆场生态修复的重要环节。本研究采用腐殖质分级和高通量测序技术,探究了秸秆和磷石膏联用对赤泥腐殖质组分和微生物群落的影响。结果表明,秸秆-磷石膏联用显著增加赤泥胡敏酸和富里酸含量,提高微生物群落多样性和丰富度,促进赤泥腐殖化过程。施用秸秆后,赤泥中葡萄糖苷酶、纤维素水解酶、多酚氧化酶和过氧化物酶分别升高7.15~8.76倍、5.64~7.12倍、2.69~4.57倍和2.59~4.24倍,显著增加Devosiaceae、Rhizobiaceae、Flavobacteriaceae、Caulobacteraceae和Cellvibrionaceae等具有纤维素降解和固氮功能微生物类群相对丰度,提高微生物群落稳定性。研究结果为外源生物质促进腐殖质累积、驱动赤泥成土进程提供科学依据。

赤泥改良过程中微生物群落及酶活性恢复研究

本研究选用蛭石、粉煤灰为基质改良剂,以园林落叶为改良基质的有机质来源,通过长期取样分析培养基质pH值、EC、CEC等基本理化指标、氮素(NO_(3)^(-)-N)含量以及微生物群落功能多样性、群落结构、酶活性等微生物指标的动态变化,来评估赤泥生态修复效果.结果表明,赤泥基质改良处理能显著降低赤泥比重,增加其孔隙率;经近1a的室外培育,基质的pH值、EC分别由11.25和1.05mS/cm降至8.49和0.27mS/cm,硝态氮含量也由8.72mg/kg增至72.17mg/kg;相应的脱氢酶、脲酶及碱性磷酸酶活性也日趋接近对照土壤,微生物群落多样性逐渐增加,群落结构显著变化,其整体代谢功能逐渐恢复.综合比较各处理的修复效果,可知在相同有机质添加量下,粉煤灰添加的处理效果优于蛭石添加,可加速赤泥的土壤化进程,为赤泥土壤化修复和规模化处理研究提供科学依据.

石膏对赤泥盐分离子迁移的影响

赤泥是氧化铝生产过程中产生的强碱性固体废弃物,盐分含量高,综合利用难。赤泥堆存的环境安全问题正严重威胁氧化铝工业的可持续发展。通过土柱淋溶模拟实验,研究不同处理(G0:不添加石膏;G2:添加2%的石膏;G4:添加4%的石膏)条件下,石膏对赤泥盐分离子迁移与分布的影响。结果表明:与G0相比,G2和G4的初渗率、稳渗率和平均渗透率分别提高31%~36%、16%~33%和9.3%~35%。G0、G2和G4渗滤液的pH值变化范围分别为8.3~9.4、8.8~10.0和9.0~9.8;EC值变化范围分别为1.0~4.0、5.8~7.2和5.2~7.5mS·cm^-1。石膏有利于渗滤液中Na^+、K^+和CO3^2-的迁移,为赤泥堆场盐分调控及赤泥土壤化处理实践提供科学依据。

石膏/蚯蚓粪肥对赤泥团聚体结构稳定性的影响

赤泥是氧化铝工业生产过程中排放的高碱性固体废弃物,迄今尚无经济有效的处置方法。以华中地区某堆场赤泥为研究对象,通过土培实验研究改良剂(石膏、蚯蚓粪肥、石膏+蚯蚓粪肥)对赤泥团聚体稳定性的影响。结果表明:石膏的添加能显著降低赤泥pH,而蚯蚓粪肥能显著增加赤泥有机碳含量。土培60d时,石膏添加后赤泥pH由10.54降到8.75,蚯蚓粪肥添加后赤泥有机碳含量由3.54g·kg-1增加至14.31g·kg^-1。土培180d时,石膏、蚯蚓粪肥、石膏+蚯蚓粪肥添加后赤泥水稳性团聚体含量由12.04%分别增加到23.49%、29.24%、33.94%;团聚体平均重量直径由0.15mm分别增加到0.26、0.30、0.34mm;可蚀性因子由0.36分别降低到0.31、0.30、0.29。石膏和蚯蚓粪肥的添加促进水稳性团聚体形成,提高赤泥团聚体稳定性。基质改良对赤泥团聚体稳定性的影响效果依次为:石膏+蚯蚓粪肥>蚯蚓粪肥>石膏。研究结果对赤泥土壤化处置和规模化消纳研究有科学参考意义。

Effect of integration of mechanical ball milling and flue gas desulfurization gypsum on dealkalization of bauxite residue

The synergistic impact of mechanical ball milling and flue gas desulfurization(FGD)gypsum on the dealkalization of bauxite residue was investigated through integrated analyses of solution chemistry,mineralogy,and microtopography.The results showed a significant decrease in Na_(2)O content(>30 wt.%)of FGD gypsum-treated bauxite residue after 30 min of mechanical ball milling.Mechanical ball milling resulted in differentiation of the elemental distribution,modification of the minerals in crystalline structure,and promotion in the dissolution of alkaline minerals,thus enhancing the acid neutralization capacity of bauxite residue.5 wt.%FGD gypsum combined with 30 min mechanical ball milling was optimal for the dealkalization of bauxite residue.

Industrial wastes applications for alkalinity regulation in bauxite residue: A comprehensive review

Bauxite residue is a highly alkaline material generated from the production of alumina in which bauxite is dissolved in caustic soda.Approximately 4.4 billion tons of bauxite residues are either stockpiled or landfilled,creating environmental risks either from the generation of dust or migration of filtrates.High alkalinity is the critical factor restricting complete utilization of bauxite residues,whilst the application of alkaline regulation agents is costly and difficult to apply widely.For now,current industrial wastes,such as waste acid,ammonia nitrogen wastewater,waste gypsum and biomass,have become major problems restricting the development of the social economy.Regulation of bauxite residues alkalinity by industrial waste was proposed to achieve‘waste control by waste’with good economic and ecological benefits.This review will focus on the origin and transformation of alkalinity in bauxite residues using typical industrial waste.It will propose key research directions with an emphasis on alkaline regulation by industrial waste,whilst also providing a scientific reference point for their potential use as amendments to enhance soil formation and establish vegetation on bauxite residue disposal areas(BRDAs)following large-scale disposal.

Variation of alkaline characteristics in bauxite residue under phosphogypsum amendment

Aiming at alkaline problem of bauxite residue,this work focused variation of alkaline characteristics in bauxite residue through phosphogypsum treatment.The results demonstrated that the pH of bauxite residue reduced from initial 10.83 to 8.70 when 1.50 wt%phosphogypsum was added for 91 d.The removal rates of free alkali and exchangeable sodium were 97.94%and 75.87%,respectively.Meanwhile,significant positive correlations(P<0.05)existed between pH and free alkali,exchangeable sodium.The effect of free alkali composition was CO3^2–>OH^–>AlO2^–>HCO3^–.In addition,alkaline phase decreased from 52.81%to 48.58%and gypsum stably presented in bauxite residue which continuously provided Ca^2+to inhibit dissolution of combined alkali.Furthermore,phosphogypsum promoted formation of macroaggregate structure,increased Ca^2+,decreased Na+and Al^3+on the surface of bauxite residue significantly,ultimately promoting soil formation in bauxite residue.

Effect of substrate amendment on alkaline minerals and aggregate stability in bauxite residue

Bauxite residue is an alkaline waste material in the process of alumina production due to its characteristics of higher salinity and alkalinity,which results in environmental issues and extremely restricts the sustainable development of alumina industries.In this work,we conduct a column experiment to study the effects of two amendments on aggregate stability and variations in alkaline minerals of bauxite residue.The two amendments are phosphogypsum(PG)and phosphogypsum and vermicompost(PVC).The dominant fraction in aggregate is 1–0.25 mm in diameter on the surface,which takes up 39.34%,39.38%,and 44.51%for CK,PG,and PVC,respectively.Additions of PG and PVC decreased pH,EC,ESP,exchangeable Na^+concentration and the percentage of alkaline minerals,and then increased exchangeable Ca^2+concentration in bauxite residue.There was significant positive correlation between pH and exchangeable Na^+concentration,the percentage of cancrinite,tricalcium aluminate and calcite;while negative correlation was found in pH value versus exchangeable Ca^2+concentration.Theses findings confirmed that additions of phosphogypsum and vermicompost have a stimulative effect on aggregate stability in bauxite residue.In particular,amendment neutralization(phosphogypsum+vermicompost)in column represents an advantage for large-scale simulation of vegetation rehabilitate in bauxite residue disposal areas.

Salt ions accumulation and distribution characteristics of pioneer plant species at a bauxite residue disposal area, China

Bauxite residue disposal areas(BRDAs)are physically degraded and hostile to plant growth.Nevertheless,natural plant colonization was observed in an abandoned BRDA in Central China.The pioneer plant species at the disposal area were identified,whilst distribution characteristics of salt ions such as Na^+,K^+,and Ca^2+in plant tissues and rhizosphere residues were investigated.The mean concentration of exchangeable Na^+in the rhizosphere soils was 19.5 cmol/kg,which suggested that these pioneer plants had relatively high salinity resistance.Sodium content varied from 0.84 cmol/kg(Digitaria sanguinalis)to 39.7 cmol/kg(Kochia scoparia),whilst K to Na ratio varied from 0.71(Myricaria bracteata)to 32.39(Digitaria sanguinalis)in the shoots,which demonstrated that the salinity tolerance mechanisms of these pioneer species differed significantly.Accumulation factors of Na^+in local plant species ranged from 0.04(D.sanguinalis)to 3.29(M.bracteata),whilst the translocation factor varied from 0.13(D.sanguinalis)to 2.92(M.bracteata).The results suggested that four pioneer plant species including K.scoparia,M.bracteate,Cynodon dactylon and D.sanguinalis could be suitable for revegetation at other disposal areas.

Rehabilitation of bauxite residue to support soil development and grassland establishment

Rehabilitation(amendment and vegetation establishment)on bauxite residue is viewed as a promising strategy to stabilize the surface and initiate soil development.However,such approaches are inhibited by high pH,high exchangeable sodium(ESP)and poor nutrient status.Amendment with gypsum is effective in improving residue physical and chemical properties and promoting seed establishment and growth.Application of organics(e.g.compost)can address nutrient deficiencies but supplemental fertilizer additions may be required.A series of germination bioassays were performed on residue to determine candidate species and optimum rehabilitation application rates.Subsequent field trials assessed establishment of grassland species Holcus lanatus and Trifolium pratense as well as physical and chemical properties of amended residue.Follow up monitoring over five years assessed elemental content in grassland and species dynamics.With co-application of the amendments several grassland species can grow on the residue.Over time other plant species can invade the restored area and fast growing nutrient demanding grasses are replaced.Scrub species can establish within a 5 Yr period and there is evidence of nutrient cycling.High pH,sodicity and nutrient deficiencies are the major limiting factors to establishing grassland on residue.Following restoration several plant species can grow on amended residue.

Regional-scale investigation of salt ions distribution characteristics in bauxite residue: A case study in a disposal area

Revegetation on bauxite residue disposal areas is the most promising strategy to reduce its potential ecological risk during stacking or disposing.Migration of salt ions in bauxite residue is one of the major issues to stimulate soil formation to support plant growth.21 residue samples were collected and the related parameters including exchangeable cations,soluble ions,total salt,pH,electrical conductivity(EC)and exchangeable sodium percentage(ESP)were selected to evaluate alkalization and salinization of bauxite residue.High levels of ions,cation exchange capacity(TOC),total salt,exchangeable sodium percentage(ESP)and cation exchange capacity(CEC)in bauxite residue were detected with greater coefficient of variation(CV),which indicated that distribution characteristics of salt ions varied significantly.The percentage of sulfate-chloride-soda type in the residues accounted for 71.43%.The mean value of pH was 10.10,whilst mean value of ESP was 52.05%.It indicated that the residues in this case study belonged to sulfate-chloride-soda saline and alkaline soil.The research results could provide theoretical basis for soil formation in bauxite residue.

Natural ripening with subsequent additions of gypsum and organic matter is key to successful bauxite residue revegetation

The processes involved in the major steps of successful revegetation of bauxite residues are examined.The first phase is the natural physical,chemical and microbial ripening of the profile.This involves allowing the profile to drain,dry,shrink and crack to depth,leaching of soluble salts,alkalinity and Na down out of the surface layers,acidification by direct carbonation and natural seeding of tolerant vegetation with an accumulation of organic matter near the surface and an attendant development of an active microbial community.Following ripening,the surface layer can be tilled and gypsum and organic matter(e.g.manures,composts,biosolids)incorporated.These amendments result in a further decrease in pH,increase in Ca and other exchangeable cations,increased leaching of Na(with a reduction in exchangeable Na and ESP),improved physical properties,particularly aggregation,and a large increase in microbial activity.Other important considerations include the choice of suitable plant species tolerant to salinity/sodicity and local environmental conditions and the addition of balanced fertilizer applications.

Dynamic change and diagnosis of physical, chemical and biological properties in bauxite residue disposal areas

Vegetation encroachment occurred in bauxite residue disposal area(BRDA)following natural weathering processes,whilst the typical indicators of soil formation are still uncertain.Residue samples were collected from the BRDA in Central China,and related physical,chemical and biological indicators of bauxite residue with different storage years were determined.The indicators of soil formation in bauxite residue were selected using principal component analysis,factor analysis,and comprehensive evaluation to establish soil quality diagnostic index model on disposal areas.Following natural weathering processes,the texture of bauxite residue changed from silty loam to sandy loam.The pH and EC decreased,whilst porosity,nutrient element content and microbial biomass increased.The identified minimum data set(MDS)included available phosphorus(AP),moisture content(MC),C/N,sand content,total nitrogen(TN),microbial biomass carbon(MBC),and pH.The soil quality index of bauxite residue increased,and the relative soil quality index decreased from 1.89 to 0.15,which indicated that natural weathering had a significant effect on improveing the quality of bauxite residue and forming a new soil-like matrix.The diagnostic model of bauxite residue was established to provide data support for the regeneration on disposal area.

Improvement of alkaline electrochemical characteristics of bauxite residue amendment with organic acid and gypsum

Neutralization of alkaline properties of bauxite residue(BR)by using organic acid and gypsum additions may effectively improve electrochemical properties and alleviate physicochemical barriers to ecological rehabilitation.Mineral acids,citric acid and hybrid acid–gypsum additions were compared for their potential to transform and improve zeta potential,isoelectric point(IEP),surface protonation and active alkaline-OH groups,which are critical factors for further improvement of physicochemical and biological properties later.Isoelectric points of untransformed bauxite residue and six transformed derivatives were determined by using electroacoustic methods.Electrochemical characteristics were significantly improved by the amendments used,resulting in reduced IEP and-OH groups and decreased surface protonation for transformed residues.XRD results revealed that the primary alkaline minerals of cancrinite,calcite and grossular were transformed by the treatments.The treatments of citric acid and gypsum promoted the dissolution of cancrinite.From the SEM examination,citric acid and gypsum treatments contributed to the reduction in IEP and redistribution of-OH groups on particle surfaces.The collective evidence suggested that citric acid and gypsum amendments may be used firstly to rapidly amend bauxite residues for alleviating the caustic conditions prior to the consideration of soil formation in bauxite residue.

Colonization of Penicillium oxalicum enhanced neutralization effects of microbial decomposition of organic matter in bauxite residue

Bauxite residue is a highly alkaline waste product from refining bauxite ore.Bioremediation driven by microbial activities has been evidently effective in lowering the alkalinity of bauxite residues,which is critical to the initiation of pedogenesis under engineered conditions.The present study investigated the changes of alkalinity and aggregation of bauxite residue at different depth in response to the colonization of Penicillium oxalicum in columns.The results demonstrated that the inoculation of P.oxalicum decreased the residue’s pH to about 7 after 30 d only at the surface layer,which was exposed to aerobic conditions.The formation of aggregates was improved overall in the organic matter treated bauxite residue.However,the EC of bauxite residue increased with time under the incubation condition,probably due to accelerated hydrolysis of sodium-rich minerals.The inoculation of P.oxalicum had no effects on urease activity,but increased cellulose enzyme activity at surface layer only.

赤泥碱性调控研究进展

赤泥是氧化铝工业生产过程产生的强碱性固体废弃物,资源化利用难、环境风险高,严重制约了氧化铝行业的可持续发展.赤泥土壤化是实现规模化处置赤泥的一种可行方法,而碱性调控则是赤泥土壤化的关键环节.论文在综述氧化铝生产过程碱性物质形成过程的基础上,从可溶性碱和化学结合碱角度分析了赤泥碱性物质的赋存状态,阐述了国内外化学调碱法和生物调碱法的研究进展和碱性转化机制,剖析了赤泥碱性调控方面存在的问题,提出了赤泥碱性调控研究的发展方向.这将为赤泥规模化处置和堆场生态重建、保障氧化铝工业的健康发展提供科学参考.