Negative effects of dissolved organic compounds on settling performance of goethite in Bayer red mud

Goethite, a typical iron-containing monomineral in red mud, was synthesized under the simulated Bayer digestion condition during the alumina production. The effects of dissolved organic compounds including sodium formate, sodium acetate, sodium oxalate, sodium salicylate and disodium phthalate on the settling performance of goethite slurries were studied. The settling performance of the slurries was also investigated with the addition of self-made hydroxamated polyacrylamide flocculant （HCPAM）. The adsorption mechanism of dissolved organic compounds on the goethite surfaces was studied by FT-IR and XPS, respectively. The results show that the addition of organic compounds lowers the settling performance of the slurries and a deterioration in settling performance is observed in the order of sodium oxalate 〉 sodium salicylate （~ disodium phthalate） 〉 sodium formate 〉 sodium acetate. Moreover, HCPAM can efficiently eliminate the negative effects of sodium formate, sodium acetate and sodium oxalate on the settling performance of the goethite slurries, but it can only partially improve the settling performance of the goethite slurries containing sodium salicylate or disodium phthalate. FT-IR and XPS results show that these organic compounds are chemically adsorbed on the goethite surface.

A 16-bit 18-MSPS flash-assisted SAR ADC with hybrid synchronous and asynchronous control logic

This paper presents a 16-bit,18-MSPS(million samples per second)flash-assisted successive-approximation-register(SAR)analog-to-digital converter(ADC)utilizing hybrid synchronous and asynchronous(HYSAS)timing control logic based on an on-chip delay-locked loop(DLL).The HYSAS scheme can provide a longer settling time for the capacitive digital-to-analog converter(CDAC)than the synchronous and asynchronous SAR ADC.Therefore,the issue of incomplete settling or ringing in the DAC voltage for cases of either on-chip or off-chip reference voltage can be solved to a large extent.In addition,the fore-ground calibration of the CDAC’s mismatch is performed with a finite-impulse-response bandpass filter(FIR-BPF)based least-mean-square(LMS)algorithm in an off-chip FPGA(field programmable gate array).Fabricated in 40-nm CMOS process,the proto-type ADC achieves 94.02-dB spurious-free dynamic range(SFDR),and 75.98-dB signal-to-noise-and-distortion ratio(SNDR)for a 2.88-MHz input under 18-MSPS sampling rate.

A Novel Clock Feedthrough Frequency Compensation for Fast-Settling of Folded-Cascode OTA

Based on the minimum settling time （MST） theory and step-response analysis of the second order system in active switched capacitor （SC） networks, a novel clock feedthrough frequency compensation （CFFC） method for a folded-cascode OTA is proposed. The damping factor r/is adjusted by using MOS capacitors to introduce clock feedthrough so that the OTA can obtain the MST state and thus achieve fast settling. Research results indicate that the settling time of the compensated OTA is reduced by 22.7% ;as the capacitor load varies from 0.5 to 2.5pF,the improved settling time increases approximately linearly from 3.62 to 4.46ns： for VGA application, fast settling can also be achieved by modifying the MOS capacitor value accordingly when the closed loop gain of the compensated OTA varies.

Yundang Lake Gets Epic Facelift

The transformation of Yundang Lake from a stinky lake to an urban reception hall has made it a showcase of ecologival restoration in China.BEFORE settling down in the City of Xiamen,Scott Patrick and his wife spent long hours searching online for just the right part of the city.When they saw Yundang Lake in west Xiamen,the couple knew they had hit the jackpot.“The picture of the beautiful lake circled by lush vegetation caught our attention.We knew this was the place we were looking for,”said Patrick.Later,after setting foot in Xiamen,he told himself he had definitely made the right life decision.

Yundang Lake Gets Epic Facelift

Before settling down in the city of Xiamen,Scott Patrick and his wife spent long hours searching online for just the right part of the city.When they saw Yundang Lake in west Xiamen,the couple knew they had hit the jackpot.“The picture of the beautiful lake circled by lush vegetation caught our attention.We knew this was the place we were looking for,”said Patrick.Later,after setting foot in Xiamen,he told himself he had definitely made the right life decision.

Roaming Where He Wants To Becoming a digital nomad in Bangkok

What makes an ideal life?For many,it’s escaping crowded and expensive big cities and the accompanying long,exhausting commutes to settle in a beautiful,warm,and budget-friendly city,or hitting the road and going elsewhere anytime you want.No alarm clocks,no punching in for work,no pressure from bosses-do a little work and then enjoy your life.This is the life for many digital nomads.

BOOKS

Quilt Arts of South Africa Edited by MARSHA MACDOWELL Indiana University Press In the far south of the African continent,women have a long tradition of crafting bed coverings using textile techniques commonly used in quilting,a practice deeply embedded in the histories of the San and Khoi peoples.Between the late 1600s and the early 1800s,South Africa experienced an influx of Dutch,French,Indian,and British settlers,including military personnel,traders,miners,and missionaries.These groups introduced their own cultural traditions,including the art of quilt making.Today,quilting thrives as a vibrant art form in South Africa.

Numerical study of flocculation settling and thickening of whole-tailings in deep cone thickener using CFD approach

Deep cone thickener (DCT) is the key equipment in cemented paste backfill (CPB), so it is essential to study the flocculation settling and thickening characteristics of the whole-tailings in DCT. Coupled with population balance model (PBM), computational fluid dynamics (CFD) was used to study the characteristics, namely particle size distribution (PSD) and underflow concentration in DCT. Based on actual production, the effects of rake rotational speed, feed rate and tailings slurry concentration were simulated and analyzed in a certain range. The PSD varied with rake rational speed, feed rate and tailings slurry concentration almost in the same trend, but the influence of feed rate was less than that of rake rational speed and tailings slurry concentration. The underflow concentration increased at first and then declined with rake rational speed and feed rate, but it rose and fell with the tailings slurry concentration. Finally, the optimal key parameters on the flocculation settling and thickening of the whole-tailings in DCT were obtained: rake rotational speed of 17 r/min, feed rate of 3.25 m^3/h and tailings slurry concentration of 20%, giving the reference values to the industrial production in Baishitamu Copper Mine.

A simple formula for predicting settling velocity of sediment particles

Based on the general relationship described by Cheng between the drag coefficient and the Reynolds number of a particle, a new relationship between the Reynolds number and a dimensionless particle parameter is proposed. Using a trial-and-error procedure to minimize errors, the coefficients were determined and a formula was developed for predicting the settling velocity of natural sediment particles. This formula has higher prediction accuracy than other published formulas and it is applicable to all Reynolds numbers less than 2× 10^5.

Coagulation enhanced electrokinetic settling of mature fine oil sands tailings

The mature fine oil sand tailings(MFT) remain as slurry in the tailings pond for long time. The dewatering and consolidation of MFT for sustainable management is an important task for the mining industry. The objective of this study is to accelerate electrokinetic settling of MFT solids in suspensions in presence of optimal coagulant. In the first phase, optimal coagulant and coagulant dosage for settling of suspension are identified, i.e., ferric chloride at 350 mg/L. It is found that the chemical treatment is not much effective; the final solid content of the sediment is only 6.48% from an initial of 5%. In the second phase,combined coagulation and electrokinetic treatment is carried out to enhance the settling effect. The direct electric current is applied in continuous and intermittent modes on MFT suspensions placed in electrokinetic cell. The results show the final solid content reaches 23.74% under the combined application of350 mg/L ferric chloride and 218.75 V/m applied voltage gradient in the continuous mode. The intermittent current mode with 40% save in power consumption produces a settled sediment having 20.84% final solid content.

Investigation on Settling Characteristics of Floes in the Changjiang Estuary, China

Settling characteristics of floes, including relative settling velocity, relative flocculation coefficient and flocculation exponent, are obtained by the suspended load equations for different size fractions. Data of the Changjiang Estuary suggest that level of flocculation changes from river section, river mouth (turbidity maximum) to offshore area in sequence of low, very high and high. The settling characteristics of floes reflected by in situ estimation performs a similar feature as that obtained from still water experiment.

Settling,consolidation and shear strength behaviour of coal tailings slurry

The volume change and shear strength behaviour of tailings slurry with the changes in gravimetric moisture content is important to effectively utilise the storage volume and analysis of dam failure potential.Consolidation testing of tailings from a slurry-like to soil-like state is a critical task,and conventional consolidation apparatus does not have the capability of doing such testing,as the tailings slurries contain high water content.Settling tests conducted on slurries having a 25%solids concentration showed very low efficiency;final sediment was still slurry-like.An intrinsic point was identified based on pore water pressure dissipation during consolidation tests in a slurry consolidometer that can define two states of the tailings i.e.slurry-like and soil-like.In the slurry-like state,the volume change was greater for Slurry 2 than Slurry 1,while the inverse was observed in the soil-like state.The evolution of peak vane shear strength with the changes in moisture content was almost similar for both samples and obeyed the power function.Regression models have been developed and validated to predict the shear strength of materials at any gravimetric moisture content or void ratio.

Negative effect of dissolved organic compounds on settling behavior of synthetic monominerals in red mud

Hydration grossular and hematite monominerals were synthesized. The effects of dissolved organic compounds(including sodium formate, sodium acetate, sodium oxalate, sodium salicylate or disodium phthalate) on the settling performance of hydration grossular or hematite slurries were studied. The settling of the slurries was also investigated with the addition of sodium polyacrylate(PAAS) or hydroxamated polyacrylamide flocculant(HCPAM). The adsorption mechanism of organic compounds on monominerals surfaces was studied by FT-IR and XPS, respectively. A deterioration in settling is observed in order of disodium phthalate>sodium salicylate>sodium oxalate>sodium formate(or sodium acetate). Moreover, PAAS can efficiently eliminate the negative effects of organic compounds on the settling performance of the hydration grossular slurry. HCPAM can efficiently eliminate the negative effects of sodium formate, sodium acetate and sodium oxalate on the settling performance of the hematite slurry, but it only partially improves the settling performance of hematite slurry containing sodium salicylate or disodium phthalate. FT-IR and XPS results show that organic compounds are physically adsorbed on hydration grossular surface, and chemisorptions of organic compounds occur on hematite surface with a bidentate chelating complex.

Observations and analyses of floc size and floc settling velocity in coastal salt marsh of Luoyuan Bay, Fujian Province, China

In coastal environments, fine-grain sediments often aggregate into large and porous flocs. ElectroMagnetic Current Meters （EMCM） and Laser In Situ Scattering and Transmissometry （LISST-ST） have been deployed within a Spartina alterniflora marsh of the Luoyuan Bay in Fujian Province, China, to measure the current velocity, the floc size and the settling velocity between 15 and 22 January 2008. During the observations, the near-bed water was collected in order to obtain the suspended sediment concentration （SSC） and constituent grain size. Data show that： （1） the nearbed current velocities vary from 0.1 to 5.6 cm/s in the central Spartina alterniflora marsh and 0.1–12.5 cm/s at the edge; （2） the SSCs vary from 47 to 188 mg/dm 3 . The mean grain size of constituent grains varies from 7.0 to 9.6 μm, and the mean floc sizes （MFS） vary from 30.4 to 69.4 μm. The relationship between the mean floc size and settling velocity can be described as： w s =ad b , in which w s is the floc settling velocity （mm/s）, a and b are coefficients. The floc settling velocity varies from 0.17 to 0.32 mm/s, with a mean value of 0.26 mm/s, and the floc settling velocity during the flood tide is higher than that during the ebb tide. The current velocity and the SSC are the main factors controlling the flocculation processes and the floc settling velocity.

Synthesis of modified polyacrylamide with high content of hydroxamate groups and settling performance of red mud

Hydroxamated polyacrylamide（HPAM） was synthesized from polyacrylamide（PAM） with high relative molecular mass under the optimum reaction conditions（p H 12 and a molar ratio of hydroxylamine to amide groups of 1.5 at 50 ℃for 12 h）. The hydroxamate groups of HPAM were verified by Fourier transform infrared spectrum（FT-IR）. 46%（molar fration） hydroxamate groups and 23%（molar fraction） carbonyl groups on HPAM were determined by conductometric titration combined with Kjeldahl＇s microanalysis method. The settling performance achieved at different flocculant dosages was investigated with high goethite-containing red mud slurry of simulated Bayer process synthesized in laboratory. It turns out that the settling performance of high goethite-containing red mud was better with HPAM. The average settling rate of red mud in the first 5 min and the turbidity of supernatant after settling for 30 min are 2.36 m/h and 507 NTU, respectively, at a flocculant dosage of 120 g/t, which is similar to that achieved with Hx-600.

Flocculated unclassified tailings settling efficiency improvement by particle collision optimization in the feedwell

Efficient thickening of tailings is a prerequisite for the metal mine tailings backfill and surface disposal operation.The effective collision of ultrafine tailings particles in suspension with flocculant molecules is essential for flocs aggregates formation and settling.Unreasonable feeding speed and flocculant adding method will lead to the failure of effective dispersion of flocculant and high particle content in thickener overflow.In this work,the effect of turbulence intensity and flocculant adding method on floc size,strength,and movement characteristics are analysed.Aiming to solve the turbidity increased,a pilot-scale continuous thickening test was carried out.Taking a single particle and multiple flocs of full tailings as the research object,the particle iterative settlement model of flocs was established.The influence of turbulence intensity on collision effect is studied by tracking and simulating particle trajectory.The results show that in the process of single particle settlement,chaos appears in the iterative process owing to particle adhesion which caused by micro action.When the turbulence intensity is 25.99%,the maximum particle size of tailings floc is 6.21 mm and the maximum sedimentation rate is 5.284 cm·s^(−1).The tailings floc presents a multi-scale structure of particle-force chain system when hindered settling,and the interweaving of strong and weak force chains constitutes the topological structure of particles.The results are applied to a thicker in plant,the flocculant addition mode and feed rate are optimized,and the flocs settling speed and overflow clarity are improved.

Numerical simulation of flocculation and settling behavior of whole-tailings particles in deep-cone thickener

Rapid dewatering and thickening of whole-tailings with ultrafine particles is one of the most important processes for the whole-tailings paste preparation. Deep-cone thickener, a kind of such process for the flocculation and settling of whole-tailings, is particularly necessary to study. However, there exist many problems in observing the flocculation and settling process of whole-tailings, as well as the particle size distribution(PSD) of whole-tailings floccules in deep-cone thickener. Population balance model(PBM) is applied to predict the PSD in deep-cone thickener, and LUO model and GHADIRI model are employed to study the aggregation and fragmentation mechanism of the whole-tailings particles, respectively. Through three-dimensional numerical simulation on the whole-tailings flocculation and settling in deep-cone thickener using computational fluid dynamics(CFD)-PBM, the distribution of density and turbulent kinetic energy in deep-cone thickener were obtained, at the same time the spatio-temporal changes of whole-tailings floccules particle size distribution are analyzed. Finally, the major flocculation position in deep-cone thickener is found and the flocculation settling rules of whole-tailings are achieved.

High molecular weight guar gum assisted settling of fine solids in diluted bitumen:Effect of solvents

As water-based extraction technologies for producing bitumen from oil sands have received increasing environmental concerns,developing non-aqueous extraction(NAE)technique is of both fundamental and practical importance.However,the relatively high concentration of fine solids trapped in the extracted bitumen presents an obstacle for pipeline transport as well as upgrading and refining downstream.This research attempts to provide a solution to fine solids removal without using synthetic additives or affecting bitumen recovery from NAE process.Herein,naturally hydrophilic additives(i.e.,water and high molecular weight guar gum(HGG)produced from Cyamopsiste tragonolobuosr L.Taup.)were introduced to promote the settling of fine solids suspended in bitumen-solvent solution,and the effects of solvents(i.e.,toluene,cyclohexane and their mixtures)were systematically investigated.Aggregate size distribution analyzed by the focused beam reflectance measurements confirmed that the addition of water and HGG could promote the agglomeration and settling of fine solids in all solvents studied.However,the size range and quantity of the agglomerates vary significantly with the solvent's aromatic character.Solvent mixtures demonstrate a superior performance on removing fine solids from bitumen over single solvent.Specifically,in a 3:2 toluene/cyclohexane mixture,the solid content was lowered from 0.66 wt%to 0.09 wt%.

A novel predictive model of drag coefficient and settling velocity of drill cuttings in non-Newtonian drilling fluids

In oil and gas well drilling operations,it is of great significance to accurately predict the drag coefficient and settling velocity of drill cuttings in non-Newtonian drilling fluids.In this paper,the free-falling of 172 groups of spheres and 522 groups of irregular-shaped sand particles in Newtonian/non-Newtonian fluids were investigated experimentally.It was found that the drag coefficient calculated based on Newtonian correlations can result in a significant error when the particle settles in the non-Newtonian fluid.Therefore,predictive models of drag coefficient were established respectively for different types of fluids.The validity of the proposed drag coefficient model of spheres was verified by comparing it with the previous works.On this basis,the drag coefficient model of irregular-shaped sand particles was established by introducing a shape factor.The models do not use the shape factor that requires detailed threedimensional shape and size information.Instead,two-dimensional geometric information(circularity)is obtained via image analysis techniques.The present new models predict the settling velocity of sand particles in the power-law fluid and Herschel-Bulkley fluid accurately with a mean relative error of5.03%and 6.74%,respectively,which verifies the accuracy of the model.

Effects of intense magnetic field on digestion and settling performances of bauxite

The effects of magnetic field intensity, roasting temperature and roasting time on digestion rate and settling performance of bauxite with different iron contents were investigated systematically. The results indicate that such magnetic treatment can profoundly change the microstructure and digestion performance of bauxite. For the two samples carrying different iron contents, phase transformation of the aluminum oxide phase proceeds faster in the high iron bauxite than the low one. The optimal pretreatment conditions of low iron bauxite are roasting temperature 550 ℃ and magnetic field intensity 6 T, while for high iron bauxite are 500 ℃ and 9 T. The digestion rate of alumina can reach 95% and 92% at digestion temperature of 190 ℃ and 250 ℃. The settling performances of roasted ore by intense magnetic field after digestion are enhanced through pretreatment.