Dynamic experiments on flocculation and sedimentation of argillized ultrafine tailings using fly-ash-based magnetic coagulant

In order to accelerate the sedimentation of super-large-scale argillized ultrafine tailings with bad features such as low settling velocity, muddy overflow water, and large flocculant dosage, a fly-ash-based magnetic coagulant （FAMC） was used in a dynamic experimental device. To obtain the best possible combination of the impact factors （magnetic intensity, FAMC dosage, flocculant dosage, and feed speed） for minimum overflow turbidity, a response surface methodology test coupled with a four-factor five-level central composite design was conducted. The synergy mechanism of FAMC and flocculant was analyzed based on the potential measurement and scanning electron microscopy. The results show that the flocculant dosage, overflow turbidity, and solid content can be reduced by 50%, 90%, and 80%, while the handling capacity per unit and efficiency of backfill and dry stacking can be promoted by 20%, 17%, and 13%, respectively, with a magnetic intensity of 0.3 T, FAMC dosage of 200 mL/t, flocculant dosage of 30 g/t, and feed speed of 0.6 t/（m^2·h）. Therefore, synergy of FAMC and flocculant has obvious efficiency in saving energy and protecting the environment by allowing 70×10^6 t/a of argillized ultrafine tailings slurry to be disposed safely and efficiently with a cost saving of more than 53×106 Yuan/a, which gives it great promise for use in domestic and foreign mines.

The effect of coupling coagulation and flocculation with membrane filtration in water treatment:A review

Water supply and sanitation demands are foreseen to face enormous challenges over the coming decades to meet the fast growing needs in a global perspective. Significant growth in the industry is predicted and membrane separation technologies have been identified as one of the possible solutions to meet future demands. Application and implementation of membrane technology is expected both in production of potable water as well as in treatment of wastewater. In potable water production membranes are substituting conventional separation technologies due to the superior performance, potential for less chemical use and sludge production, as well as the potential to fulfill hygienic barrier requirements. Membrane bio-reactor （MBR） technology is probably the membrane process which has had most success and has the best prospects for the future in wastewater treatment. Trends and developments indicate that this technology is becoming accepted and is rapidly becoming the best available technology for many wastewater treatment applications. A major drawback of MBR systems is membrane fouling. Studies have shown that fouling mitigation in MBR systems can potentially be done by coupling coagulation and flocculation to the process.

Flocculation performance of a novel synthesized flocculant with low ecological risk

Combined flocculants with low ecological risk are urgently required in water supply and wastewater treatment in China. A novel flocculant was thus developed under the condition of low ecological risk(noted as CAS). The experiments to examine wastewater treatment performance of the new product showed that there was favourable performance in the flocculation process in contrast to commercial flocculants in treating kaolin suspensions, municipal effluent and domestic wastewater. Flocculation performance included the turbidity removal rate, sediment character and a decrease in COD(chemical oxygen demand). The sediment time of flocculation is short and the removal rate of turbidity treated by CAS is high compared with PAC(polyaluminum chloride), PAM(polyacrylamide) and the combined addition of PAC and PAM. The optimal concentration required to affect flocculation processes is dependent on kaolin concentration and the character of the wastewater within the range examined. It also showed that CAS is effective to treat wastewater with high turbidity.

Theory on Orthokinetic Flocculation of Cohesive Sediment: A Review

Investigation on flocculation phenomenon of cohesive fine-grained sediment has been a important part of sediment dynamics. During all of three dynamical factors (i.e., Brownian motion, flow shear and differential settling) that have been verified to play important roles in promoting flocculation of cohesive sediment, the influence of flow shear on sediment flocculation has been paid great attention by many researchers (this flocculation pattern has been termed as “orthokinetic flocculation” in most of published literatures). Among many researches regarding orthokinetic flocculation, the dynamical equation developed by Smoluchowski in 1917 (we called it as Smoluchowski equation hereafter) has been widely adopted as an origin and basement for theoretically analyzing sediment flocculation under a shear flow. Meanwhile, many researchers have also pointed out the deficiencies of Smoluchowski equation (this is because the derivation of Smoluchowski equation was based on six different assumptions), and correspondingly have amended this equation from different aspects. In this paper, we attempt to summarize these results, hopefully providing the theoretical research of sediment orthokinetic flocculation with some references.

Flocculation properties of cohesive fine-grained sediment in the Three Gorges Reservoir under variable turbulent shear

Sediment flocculation is a key process for the deposition of fine-grained sediments in the Three Gorges Reservoir(TGR)of China.Sediment flocculation influences the evolution of the river regime,but also hampers the smooth navigation in the long term.However,the flocculation process and its controlling factors are poorly understood.We experimentally determined the flocculation properties of cohesive sediment of samples from the TGR(predominantly a mixture of clay and silt)over a range of turbulent shear rates and sediment concentrations.The experiments were conducted in an almost isotropic turbulence field,which was simulated by an array of horizontal oscillating grids in a water tank.Sediment flocculation was recorded by a camera and investigated by image analysis.Our new data indicate that flocculation is generally a response in equilibrium median floc size(d_(f,50))to the increase of the shear rate G.The peak value is attained at G=16.5 s^(-1),where d_(f,50) is 81.3μm(for the suspended sediment concentration(ssc)=0.4 g/L)and 107μm(for ssc=0.7 g/L),respectively.At low shear rates(G<16.5 s^(-1)),the equilibrium floc sizes d_(f,50) increase with rising shear rate G and isinversely related to the Kolmogorov micro length scale η.We attribute this variability to an insufficient deposition time of the sediment flocs in the water tank.Settling velocities,calculated from our experimental data of the floc sizes,are almost consistent with in-situ measured settling velocities,and are ten times larger than the terminal settling velocity of primary particles as calculated from Stokes'law.

Cellulosic Sorption Filter Materials with Surface Flocculation Activity—A Hopeful Anticipation of Water Purification

A filter media was developed comprising ionic activated cellulosic material with enormous sorption activity to ions-active dissolved and colloidal substances in aqueous systems evoking so-called surface flocculation and a filling material having a filter effect. The dilemma of the art of low sorption efficiency and high flow rate of filtrated aqueous dispersions without sacrificing its separation efficiency of fines has been solved by use of activated cellulosic material having multi-fold (roughly tenfold to hundredfold) sorption capacity for ions-active dissolved and submicron particulate contaminants compared to untreated cellulosic material.

Influence of coarse tailings on flocculation settlement

The composition of tailings particles in mines plays a key role in the flocculation settlement of slurries.To study the influence of coarse particle tailings(CPTs)on the flocculation settlement of tailings slurries(TSs),static flocculent settling tests,scanning electron microscopy observations,and laser particle size analyses were conducted using the tailings obtained from a copper mine.The results demonstrate that(i)in the accelerated and free settling process,CPTs did not directly settle at the bottom of graduated cylinders;instead,they were netted by the flocculent structures(FSs)and settled together more quickly.The CPTs accelerate the rapid settlement of TSs;the acceleration effect is more obvious when the CPTs content is greater than 50 wt%.(ii)The most appropriate flocculant unit consumption(FUC)is 20 g·t-1,and no substantial increase is observed in the flocculant settling velocity with an increase in the flocculant because the effective FSs did not substantially change and thus did not lead to a notable increase in the settling velocity of the solid–liquid interface(SLI).(iii)In the effective settling space of the thickening facility,free water quickly flowed from the pores of FSs,which is reflected in the period from 0 to 1 min.

Analysis of floc morphology in a continuous-flow flocculation and sedimentation reactor

The floc morphology was investigated in a continuous-flow reactor, in order to understand the evolution of flocs in practical flocculation and sedimentation processes in water utilities. Kaolin-humic acid suspension was used as the test water, and polyaluminum chloride was chosen as the coagulant. An in-situ recognition system was applied to analyze the floc size, boundary fractal dimension, and eccentricity ratios. Particle numbers and turbidity were also determined in the sedimentation stage. At a coagulant dose of 1 mg/L as Al, the average floc size increased from 62 to 78 μm and the boundary fractal dimension was around 1.14, suggesting that flocs were compact and continuously grew during the entire flocculation process. However, with the dose increased to 5 mg/L, the average floc size decreased and stabilized at around 65 μm, with the fractal dimension of 1.20. It can be concluded that the excess coagulant doses resulted in the formation of chain-shaped, lower density, and more branched structure flocs, thereby restricting flocs’ further growth in the subsequent flocculation. Floc morphology analysis suggested that charge neutralization dominated in the initial flocculation stage, then the bridge and sweep mechanisms were dominant in the subsequent flocculation. In addition, compared with the traditional inclined plate settler, a novel V-shaped plate settler introduced in this study had an advantage in small size floc（less than 5 μm） removal. The V-shaped region could promote aggregate restructuring and re-flocculation; therefore, the V-shaped plate settler provides an alternative method for sedimentation.

Sedimentation acceleration of remanent iron oxide by magnetic flocculation

Sedimentation based processes are widely used in industry to separate particles from a liquid phase. Since the advent of the ＂Nanoworld＂ the demand for effective separation technologies has rapidly risen, calling for the development of new separation concepts, one of which lies in hybrid separation using the superposition of a magnetic field for magnetic particles. Possible product portfolio of such separation consists of pigment production, nanomagnetics production for electronics and bio separation, A promising step in that direction is magnetic field enhanced cake filtration, which has by now progressed from batch to continuous ooeration. In sedimentation processes in a mass force field the settling behaviour of particles strongly depends on physico-chemical properties, concentration and size distribution of the particles. By adjusting the pH, the interparticle forces, in particular the electrostatic repulsion, can be manipulated. For remanent magnetic particles such as magnetite, pre-treatment in a magnetic field could lead to a change of interparticle interactions. By magnetizing the particles apart from van der Waals attraction and electrostatic repulsion, an additional potential is induced, the magnetic attraction, which could easily dominate the other potentials and result in agglomeration in the primary minimum. By sedimentation analysis, a wide spectrum of parameters like pH, magnetic field strength and concentration have been investigated. The results show a strong increase of sedimentation velocity by magnetic flocculation of the raw suspension. This leads to a rise in throughput due to the acceleration of sedimentation kinetics by imparting a non-chemical interaction to the physico-chemical properties in the feed stream of the separation apparatus.

The Characteristics of Dynamics and Sedimentation in the Mouth Area of Xiashimen Strait Channel, Zhejiang , China

According to the hydrographic and sediment data, the dynamic sedimentation characteristics are dealt with based on the analyses of the hydra-dynamics and the suspended and bottom sediment characters in Xiashimen (XSM) strait channel mouth area in the eastern part of Zhoushan Islands. It is pointed out that both of the changes of the hydra-dynamics and the fine sediment supply from Changjiang estuary result in the sedimentation mechanism of mainly the fine sediments flocculating deposition and secondly the coarser sediment deposition in single grain. The dynamic sedimentation characteristics are developed under the action of the deposition mechanism and reworking differences in different bedform areas.

Physicochemical interaction and its influence on deep bed filtration process

The capillary model was used to analyze the hydraulic conditions in the deep bed filtration process. The physicochemical interaction forces between the filter media and suspended particles and their influence on deep bed filtration process were also studied theoretically. Through the comparison of the hydraulic and physicochemical forces, the key influencing factors on the filtration process were proposed and investigated. Pilot study of the micro-flocculation deep bed filtration was carried out in the No. 9 Potable Water Treatment Plant of Beijing, and the experimental results of hydraulic head loss, particle distribution and entrapment were presented. The theoretical prediction was reasonably consistent with the experimental results under different conditions, which indicated that the regulation and control of micro-flocculation and deep bed filtration could be realized by the evaluation of the physicochemical interactions. Further theoretical and experimental research should be carried out to investigate the interaction mechanism and its application in the deep bed filtration and other cases.

DUAL FILTRATION EFFECT OF GEOCHEMICAL AND BIOGEOCHEMICAL PROCESSES IN THE CHANGJIANG ESTUARY

Dissolved nutrients (NO3- , PO4 3- , SiO32- ) and oxygen , chlorophyll- a , pH and Eh were measured on board during a cruise in August 1988 in the Changjiang Estuary region . Heavy metals , organic matter and carbonate contents were analyzed in laboratory. The results show that geochemical processes in the Changjiang Estuary have dual filtration effect: on the one hand geochemical filtration effect, reflected by ferromanganese oxide flocculation and sedimentation , occurs near the turbidity maximum, and leads to enrichment of heavy metals in suspended matter and sedi -ments; on the other hand biogeochemical filtration , reflected by nutrients consumption , organic matter and carbonate sedimentation and enrichment of trace elements in suspended matter. occurs outside the plume water front. The biogeochemical filtration affects the environmental conditions ; the dissolved oxygen and pH increase in surface water and decrease in bottom water. The biogeochemical filtration effect outside the plume front is

不同类型铁矿粉湿式磨矿—沉降—过滤行为及其影响因素分析

湿式磨矿—沉降—过滤工艺是目前国内钢厂常用的粗粒铁矿粉细磨制备合格球团原料的方法,而铁矿粉性质直接影响磨矿能耗、沉降—过滤性能及整个原料预处理工序的效率。本文以5种不同类型铁矿粉为研究对象,对其湿式磨矿、沉降和过滤行为进行研究,并分析铁矿粉湿式磨矿、沉降和过滤性能的影响因素。研究结果表明:铁矿粉的可磨性可基于矿石硬度特性进行评估和预测,矿石硬度越大,磨矿能耗越高;影响球磨后铁矿沉降性能的主要因素有矿粉颗粒的粒度、密度和表面粗糙程度等;当磨矿时间越长,粒度越小(尤其是粒度低于0.045 mm的细粒级颗粒)质量分数越高,沉降速率越低;同时,粒度低于0.045 mm的细粒级颗粒质量分数也是影响矿浆过滤性能的主要因素之一,颗粒粒度越小,过滤性能越差,滤饼残余水分越高,说明在实际生产中应优化和确定适宜的球团精矿粒度,避免铁矿粉在湿磨阶段产生过磨现象,进而降低沉降和过滤效率。本研究可为球团企业提高原料预处理效率和降低球团生产成本提供参考。

Experimental investigation of the inhibition of deep-sea mining sediment plumes by polyaluminum chloride

Deep-sea sediment disturbance may occur when collecting polymetallic nodules,resulting in the creation of plumes that could have a negative impact on the ecological environment.This study aims to investigate the potential solution of using polyaluminum chloride(PAC)in the water jet.The effects of PAC are examined through a self-designed simulation system for deep-sea polymetallic nodule collection and sediment samples from a potential deep-sea mining area.The experimental results showed that the optimal PAC dose was found to be 0.75 g/L.Compared with the test conditions without the addition of PAC,the presence of PAC leads to a reduction in volume,lower characteristic turbidity,smaller diffusion velocity,and shorter settling time of the plume.This indicates that PAC inhibits the entire development process of the plume.The addition of PAC leads to the flocculation of mm-sized particles,resulting in the formation of cm-sized flocs.The flocculation of particles decreases the rate of erosion on the seabed by around 30%.This reduction in erosion helps to decrease the formation of plumes.Additionally,when the size of suspended particles increases,it reduces the scale at which they diffuse.Furthermore,the settling velocity of flocs(around 10^(-2) m/s)is much higher that of compared to sediment particles(around 10^(-5) m/s),which effectively reduces the amount of time the plume remains in suspension.

基于投影寻踪回归方法的微压过滤冲洗池水头损失与过滤效率预测模型

以微压过滤冲洗池的水头损失与过滤效率为考核指标,考虑进水流量、矿化度、含沙量与滤网孔径4个因素进行正交试验设计,采用投影寻踪回归方法PPR分析各个因素对考核指标的影响权重,选取20组试验数据建立含沙微咸水条件下微压过滤冲洗池水头损失和过滤效率的预测模型,探究了含沙微咸水对微压过滤冲洗池的水头损失和过滤效率的影响。研究结果表明,影响微压过滤冲洗池水头损失的因素由大到小依次为进水流量、含沙量、矿化度、滤网孔径;影响过滤效率的因素由大到小依次为含沙量、进水流量、矿化度、滤网孔径;构建的PPR预测模型的预测精度整体合格率达100%;当进水流量为6~7 m^(3)/h、含沙量为0.5~1.0 g/L、矿化度为0~2.0 g/L及滤网孔径为0.125~0.180 mm时,水头损失存在最小值;当进水流量为9~10 m^(3)/h、含沙量为1.75~2.00 g/L、矿化度为0~3.0 g/L及滤网孔径为0.125~0.150 mm时,过滤效率存在最大值。物理模型的试验结果可为微压过滤冲洗池的实际应用提供研究基础。

Rainwater utilization and storm pollution control based on urban runoff characterization

The characteristics of urban runoffs and their impact on rainwater utilization and storm pollution control were investigated in three different functional areas of Zhengzhou City, China. The results showed that in the same rain event the pollutant loads （chemical oxygen demand （COD） and total suspended solids （TSS）） in the sampling areas were in the order of industrial area 〉 commercial area 〉 residential area, and within the same area the COD and TSS concentrations of road runoffs were higher than those of roof runoffs. The first flush effects in roof and road runoffs were observed, hence the initial rainwater should be treated separately to reduce rainwater utilization cost and control storm pollution. The initial roof rainfall of 2 mm in residential area, 5 mm in commercial area and 10 mm in industrial area, and the initial road rainfall of 4 mm in residential area and all the road rainfall in commercial and industrial areas should be collected and treated accordingly before direct discharge or utilization. Based on the strong correlation between COD and TSS （R2, 0.87-0.95） and the low biodegradation capacity （biochemical oxygen demand BOD5/COD 〈 0.3）, a sedimentation process and an effective filtration system composed of soil and slag were designed to treat the initial rainwater, which could remove over 90% of the pollutant loads. The above results may help to develop better rainwater utilization and pollution control strategies for cities with water shortages.

某铀矿高钙矿浆絮凝沉降工艺优化试验研究

针对某铀矿高钙矿浆固液分离中存在的矿浆沉降速度较低、固-液分离效果变差等问题,研究采用了静态絮凝法沉降该铀矿高钙矿浆,考察了絮凝剂种类及用量、混合絮凝剂配比及加入方式对沉降效果的影响。结果表明:由WZ944絮凝剂与5330絮凝剂配制的混合絮凝剂可使高钙矿浆沉降速度显著提高,2种絮凝剂的最佳质量配比为1∶1,混合絮凝剂最低用量为35g/t。试验结果可为该铀矿固-液分离工艺流程优化设计提供参考。

MIXING OF SALT WATER AND FRESH WATER IN THE CHANGJIANG RIVER ESTUARY AND ITS EFFECTS ON SUSPENDED SEDIMENT

Using field hydrological data, the relationship between the mixing of salt water and fresh water and the tidal range/ high tidal level in the Changjiang (Yangtze) River estuary is discussed, and the transporting and concentrating of suspended sediment in the estuary were also analysed in respect to the circulation, flocculation and stratified interface resulting from mixing.The calculation results by two-dimentional box model have confirmed the effects of the circulation on the concentrating of suspended sediment in the estuary. The conclusions derived from this work have deepened the understanding on the mixing in the Changjiang River estuary and are of significance in bo’th theory and practice.

塔河下游高含沙浑水絮凝沉降试验研究

细粒悬移质高含沙浑水对微灌系统的淤堵一直困扰着区域节水灌溉的推行和农业节水能力的提升。以典型的塔里木河高含沙浑水为例,选用5种不同浓度的絮凝剂,以泥沙沉降比、淤积泥沙的体积、上清液浊度、处理成本等参数为指标,应用层次分析法及熵权法耦合得到各参数综合权重,优选去除细粒泥沙的最佳组次。试验结果表明,考虑絮凝沉降效果、絮凝剂成本、泥沙浑浊液的浊度和絮凝物的体积等因素,阴离子聚丙烯酰胺PAM(-)沉降效果最好;泥沙浓度为12%,PAM(-)的添加量为0.01 g/L为试验组次最优。试验结果可为塔河中下游灌区高含沙浑水絮凝沉沙提供参考。

油田井场污水多价阳离子处理技术研究

油田井场污水组成复杂且含有多种多价离子,直接外排不仅污染周围环境,也无法实现节约水资源和回收利用的目的。综述了油田污水中多价离子的各种处理技术,包括化学沉淀、混凝/絮凝、螯合/络合、屏蔽/掩蔽等;对不同处理技术的优劣势和适用条件进行了对比分析;最后对油田井场污水多价离子处理技术未来的研究方向进行了展望,总结提出:应迎合绿色化学思路,着重开展微生物和生物膜污水处理技术研究,并大力发展复合絮凝剂及多功能多价离子处理剂技术。