Fate of sulphate removed during the treatment of circumneutral mine water and acid mine drainage with coal fly ash: Modelling and experimental approach

The treatment of acid mine drainage (AMD) and circumneutral mine water (CMW) with South African coal fly ash (FA) provides a low cost and alternative technique for treating mine wastes waters. The sulphate concentration in AMD can be reduced significantly when AMD was treated with the FA to pH 9. On the other hand an insignificant amount of sulphate was removed when CMW (containing a very low concentration of Fe and Al) was treated using FA to pH 9. The levels of Fe and Al, and the final solution pH in the AMD–fly ash mixture played a significant role on the level of sulphate removal in contrast to CMW–fly ash mixtures. In this study, a modelling approach using PHREEQC geochemical modelling software was combined with AMD–fly ash and/or CMW–fly ash neutralization experiments in order to predict the mineral phases involved in sulphate removal. The effects of solution pH and Fe and Al concentration in mine water on sulphate were also investigated. The results obtained showed that sulphate, Fe, Al, Mg and Mn removal from AMD and/or CMW with fly ash is a function of solution pH. The presence of Fe and Al in AMD exhibited buffering characteristic leading to more lime leaching from FA into mine water, hence increasing the concentration of Ca²⁺. This resulted in increased removal of sulphate as CaSO₄·2H₂O. In addition the sulphate removal was enhanced through the precipitation as Fe and Al oxyhydroxysulphates (as shown by geochemical modelling) in AMD–fly ash system. The low concentration of Fe and Al in CMW resulted in sulphate removal depending mainly on CaSO₄·2H₂O. The results of this study would have implications on the design of treatment methods relevant for different mine waters.     

碱改性粉煤灰处理含铬废水

采用碱改性方法改性粉煤灰,通过单因素试验处理含铬废水,并对操作条件进行选择和优化,单因素试验表明当投灰量60 g/L,pH值14,吸附时间60 min,吸附温度为20℃,Cr~(6+)初始浓度为40μg/m L的条件下,Cr~(6+)去除率可达92.72%。吸附机理试验表明碱改性粉煤灰吸附含铬废水的过程符合Freundlich吸附等温方程。     

粉煤灰沸石的微波合成

以粉煤灰为原料,在微波辐射条件下,采用多段技术合成了NaP1型和NaA型沸石,考察并讨论了氢氧化钠的浓度、液固比以及添加剂等对沸石产品的阳离子交换性能（CEC）的影响.研究结果表明, 沸石产品的CEC值随着氢氧化钠浓度的升高和液固比的增加呈增加趋势,至氢氧化钠浓度为2 mol/L和液固比为8 mL/g时达到最大值.在此最佳条件下,NaP1和NaA两种沸石产品的CEC值分别为159.2 mmol/100 g和157.7 mmol/100 g.NaF、十六烷基三甲基溴化铵和95%乙醇等3种添加剂可以明显地改善NaP1和NaA两种沸石产品的CEC值.研究结果显示,微波多段合成技术在沸石合成过程中起到了重要的作用,不仅缩短了合成时间,而且保持了产品的高离子交换性能.     

平顶山矸石电厂粉煤灰特征及其综合利用

本文采用化学分析、x射线衍射、电镜、28天抗压强度技术手段,对平顶山矸石电厂的粉煤灰样品进行了分析;结合有关国家标准和文献,对矸石电厂粉煤灰进行分类,并对其综合利用途径做出评价。     

Properties of fly ash stabilized haul road construction materials

ABSTRACT

Larger haul trucks are being used at surface mines in Canada thus requiring better haul roads to carry heavier loads. The availability of good quality aggregate to build haul roads is limited for prairie coal mines. However, most of these mines are located adjacent to coal-fired electrical power plants, which produce by-product fly ash as a waste. Fly ash can be used to increase strength and stiffness of soil and road bases.

Unconfined compressive strength tests conducted on various mixtures of fly ash, kiln dust, mine spoil, and coal seam partings showed that the cementing characteristics of unclassified fly ash from central Alberta coals was low. However, the addition of cement kiln dust, which is high in CaO, enabled the fly ash to exhibit significant cementing action.

Mixtures of fly ash, kiln dust, and mine spoil or coal seam partings had unconfined compressive strengths of about 1 MPa and elastic moduli of about 350 MPa after 14 to 28 days. This compares favourably with compacted mine spoil or coal seam partings which have estimated unconfined compressive strengths of less than 0.4 MPa and moduli of about 50 MPa. Thus fly ash stabilized mine spoil or coal seam partings were found to have potential for use in constructing haul road base and sub-base layers since maximum tire pressures on the running surface are less than 0.7 MPa.     

粉煤灰中难浮未燃炭的柱式浮选脱除试验研究

采用粒度分析、X射线衍射、接触角测量和X荧光分析等手段对矿样的物理化学性质进行表征,从表面性质的角度探讨未燃炭可浮性较差的内在原因;研究黏性起泡剂KD对浮选体系的泡沫稳定作用;采用实验室型旋流-静态微泡浮选柱研究未燃炭的柱式浮选行为。研究结果表明：黏性起泡剂可有效提高浮选体系的泡沫稳定性,在起泡剂KD用量400 g/t、表观充气速率1.8 cm/s、泡沫层厚度150～200 mm、浮选柱循环压力0.22 MPa的优化试验条件下,可以得到烧失量3.15%的低炭灰产品,炭脱除率达91.88%。     

粉煤灰制多孔玻璃微珠

摘要：以电厂的废弃物粉煤灰为原料,研究了1273K温度下,粉煤灰和添加剂粉末制得了孔隙率较高的多孔玻璃微珠的过程。并对其吸附性能做了初步研究。用氮吸附静态容量法,测得该多孔玻璃微珠的氮吸附等温线、比表面和孔分布曲线。探讨了多孔玻璃微珠吸附特性和成珠条件。     

粉煤灰中未燃炭回收的试验研究

用粒度分析、X射线衍射和X荧光分析等手段对山西某电厂的粉煤灰的物理化学性质进行分析。对试验样进行了浮选机探索试验和浮选柱工艺优化试验。研究结果表明,优化工艺条件为柴油捕收剂用量400 g/t,起泡剂用量400 g/t,矿浆浓度15%,循环压力0.10 MPa,泡沫层高度3 cm,可得到产率为75.99%的尾灰,烧失量为1.17%,精煤产率为24.01%,烧失量为52.47%。在尾灰烧失量达到一级粉煤灰的指标要求下,柱式浮选的产率要高于浮选机的产率。     

Adsorption of Pb(II), Zn(II) and Cr(III) on coal fly ash porous pellets

In the present work the application of fly ash porous pellets as adsorbent of lead(II), zinc(II) and chromium(III) ions from aqueous solution was studied. Experiments were carried out using porous pellets developed from fly ash derived from Megalopolis, Greece coal-burning power plant. The material was shaped into spherical agglomerates, after wetting and tumbling in a laboratory scale granulator. The adsorption of heavy metals on fly ash pellets was studied as a function of the initial metal concentration, solution pH and temperature. Kinetic studies indicated that sorption follows a pseudo-second-order model. Adsorption isotherms of lead, zinc and chromium were determined for agglomerated material using the Langmuir equation. The adsorption capacity of fly ash pellets reached at 0.22 mmol Pb/g pellet, 0.27 mmol Zn/g pellet and 0.44 mmol Cr/g pellet. Furthermore adsorption from bimetallic solutions (Cr–Zn, Cr–Pb and Pb–Zn) took place in order to study presumable antagonistic effects on adsorption of heavy metals. Finally, the stabilization of metal saturated pellets was studied. The stabilization procedure took place in structures made of concrete, where 75% of cement was replaced by raw fly ash. The evaluation of the procedure through leaching tests showed excellent heavy metals stabilization in concrete blocks.     

浮选法脱除粉煤灰中未燃碳的研究

为提高粉煤灰资源化利用水平和有效保护环境,对广东坪石发电厂粉煤灰的粒度特性和未燃碳的粒级分布进行分析,并采用接触角测量仪分析未燃碳粒的表面疏水性,基于此进行浮选脱碳试验。试验结果表明:该粉煤灰粒度极细,<0.074 mm粒级产率约为89.81%,未燃碳粒接触角仅为21°,可浮性差;当柴油用量为10 kg/t、仲辛醇用量为3.5 kg/t时,浮选尾煤产率为73.85%,烧失量为4.89%,浮选精煤产率为26.15%,灰分为45.45%,发热量为14.34 kJ/kg,综合回收率较高。     

Effect of fly ash characteristics on the behaviour of pastes prepared under varied brine conditions

To meet the escalating demand of energy more coal ash and brines are inevitably produced as by-products. Large volumes of these wastes and increasing environmental awareness necessitate the development of more sustainable methods to mitigate the environmental footprint. Paste backfill is one of the potential solutions to keep the energy industry sustainable. The behaviour of pastes was investigated by strategically varying brine composition mixed with the two types of fly ash. The results showed that fly ash plays a more prominent role in the behaviour of pastes than brines. It is therefore imperative to consider both fly ash and brine characteristics i.e. constituents of paste for the development of an environmentally sound paste backfill practice. Technically there are numerous benefits in pursuing the proposed solution.     

粉煤灰对煤矸石酸性重金属淋滤液的修复作用

采用批处理吸附实验和柱状淋溶模拟实验,分析粉煤灰吸附重金属、处理煤矸石酸性重金属淋滤液的效果及机理。结果表明：① 粉煤灰对Pb2+、Cu2+、Cd2+ 和Zn2+的吸附等温线符合Freundlich等温模式,吸附过程符合准二级反应动力学模型,且均在30 min内达到吸附平衡,随着pH增加,4种重金属离子吸附率逐渐增加并趋于平衡（Pb、Cu、Cd、Zn分别在pH=3.5、6.0、7.5、8.0时达到平衡）,在酸性环境下粉煤灰对4种金属离子具有较好的吸附性能;② 在重金属竞争性吸附中,共存离子的存在抑制了目标离子的吸附,其中Pb受共存离子的影响最小,粉煤灰吸附强弱顺序为Pb>Cu>Cd>Zn;③ 煤矸石柱状淋溶试验中,煤矸石淋滤液呈现较强酸性、较高重金属浓度的酸性矿山废水特征,而在粉煤灰处理中,淋滤液的pH值呈中性,重金属离子浓度显著下降,其主要机制为粉煤灰吸附、碱性中和、重金属与Fe共沉淀等。研究表明,实验用粉煤灰具有修复煤矸石酸性重金属淋滤液的潜力。     

不同加碱活化方法对粉煤灰合成沸石的影响

粉煤灰中含有一些活性较差的莫来石和石英结晶体,在直接水热条件下,它们很难参与沸石晶体的合成反应,严重影响了粉煤灰合成沸石晶体产品的纯度和结晶度。通过对湿法加碱-煅烧和干法加碱-煅烧两种活化方法的比较,证明了湿法加碱-煅烧方法不仅完全消除了粉煤灰中原有的结晶,生成了大量高活性的硅铝酸盐矿物,而且能在后续的水热合成过程中促进沸石向单晶转化。本文的研究对粉煤灰合成高质量沸石晶体具有一定的指导作用。     

Application of coal fly ash to circumneutral mine waters for the removal of sulphates as gypsum and ettringite

South African power stations generate large amounts of highly alkaline fly ash (FA). This waste product has a serious impact on the environment. Acid mine drainage (AMD) is another environmental problem associated with mining. AMD has high heavy metal content in addition to high sulphate concentrations. Several studies have shown that 80–90% of sulphates can be removed when FA is co-disposed with AMD rich in Fe and Al. In South Africa, sources of contaminated mine waters, unlike AMD have circumneutral pH and much lower concentrations of Fe and Al, but rich in Ca and Mg. Treatment of such waters with FA resulted in no significant removal of sulphates when treated to pH less than 10. Subsequent treatment of circumneutral mine water to pH greater than 11 resulted in more than 60% sulphate removal. Treatment of circumneutral mine water to pH greater than 11 with FA followed by seeding with gypsum crystals and the addition of amorphous Al(OH)₃ resulted in removal of sulphate to levels below the Department of Water Affairs and Forestry (DWAF) water quality effluent limit (500 ppm).     

煤矿电厂粉煤灰光催化特性的研究

以太阳光、紫外灯、高压汞灯为激发光源,以甲基橙为试验废水,采用BET,XRD为表征手段和Langmuir-Hinshewood动力学方程方法,研究粉煤灰光催化特性.实验结果表明,无光照下粉煤灰吸附甲基橙符合Langmuir等温吸附经验式1/q_t=0.653 9+0.454 4/C_e.在光激发下粉煤灰处理甲基橙溶液,脱色率普遍提高1%～9%,以太阳光的光催化活性最大.说明粉煤灰玻璃微珠表面的Fe₂O₃可吸收太阳光中的可见光,具有光活性.无光照下其吸附速度常数与有光源激发时表观一级反应速度常数有差异.对粉煤灰光催化活性的主要影响因素是：波长、投灰量、溶液初始的pH值.     

混煤燃烧过程中飞灰颗粒排放特性试验

为了解混煤燃烧对飞灰颗粒尤其是超细颗粒排放特性的影响,在一维沉降炉上对平朔、大优及神木3种烟煤及其混煤进行燃烧试验.采用激光粒度分析仪对收集的飞灰颗粒尺寸分布进行测定,并对混煤飞灰颗粒的体积平均直径及可吸入颗粒物（PM₁₀）、超细颗粒物（PM_2.5）所占比例的计算值与测量值进行比较.结果表明：合理混煤能增大飞灰颗粒的粒径,减少可吸入颗粒物（PM₁₀）及超细颗粒物（PM_2.5）的排放;混煤的飞灰颗粒粒径分布受组成煤种、灰分含量及煤灰成分等因素的影响.     

粉煤灰在煤矿软岩巷道支护中的应用技术

为了综合利用粉煤灰,降低软岩巷道锚注支护的成本,就粉煤灰在煤矿软岩巷道支护中的应用技术进行了研究,采用水泥与粉煤灰体积比为1:1的注浆材料代替纯水泥浆来改进锚注支护中的注浆材料.应用粉煤灰对火烧铺矿围岩进行了加固,并对经粉煤灰加固后的巷道围岩进行了实地开挖观察发现,巷道的收敛变形情况和巷道围岩凝结情况均达到了用纯水泥作注浆材料的加固支护效果,巷道维修周期与单纯的锚网和架棚相比可延长6倍以上,取得了较好的技术经济效果.     

粉煤灰混凝土的耐久性研究

研究了影响粉煤灰混凝土耐久性(抗渗性、抗冻性、抗碳化性、抗氯离子侵蚀性)的因素,通过理论分析指出掺粉煤灰改善了混凝土的耐久性,粉煤灰的三种基本效应即形态效应、活性效应、微集料效应是粉煤灰混凝土耐久性提高的重要因素。     

粉煤灰中氧化铝浸取模型的建立

从粉煤灰中浸取氧化铝的工艺参数入手,对氧化铝浸取模型建立进行了研究.通过正交试验分别构建Na₂CO₃溶液与自粉化料比、Na₂CO₃溶液浓度、浸取温度、浸取时间等因素对氧化铝浸取率影响的回归方程,确定各因子相关系数,建立浸取过程的数学模型.检验结果表明,该数学模型对不同品质的粉煤灰具有较好的适应性,实验误差在5％以内,具有一定的可信度.应用模型可以进行最佳工艺参数设置,提高工程放大倍数,减少试验工作量,降低研究开发成本.     

无机盐阳离子对粉煤灰浮选泡沫稳定性的影响研究

粉煤灰中矿物组成的自然属性使得浮选脱炭体系的泡沫稳定性较差,从而影响了未燃炭的有效脱除。通过添加无机盐阳离子的方式来改变粉煤灰浮选矿浆体系的液相性质,研究了不同离子种类和含量对两相泡沫和粉煤灰浮选三相泡沫稳定性的影响,并进行了浮选验证。研究结果表明：无机盐阳离子的添加提高了泡沫的稳定性,阳离子价态越高,这种稳定作用就越明显。利用泡沫稳定性调节中的离子效应,对采自湖北黄石的粉煤灰样品进行了浮选脱炭的验证试验,结果表明：Fe3+对泡沫的稳定作用有效提高了粉煤灰的浮选脱炭效果,与空白浮选体系相比,在Fe3+浓度为3 mmol/L的条件下,浮选低炭灰烧失量由8.85%降低至5.57%,炭脱除率由41.94%提升至74.55%;与添加Fe3+的浮选体系相比,Mg2+和Na+对浮选指标的提高作用依次减弱。