有机高分子絮凝剂在污泥脱水中的应用

随着污泥成分的复杂化，与无机絮凝剂相比有机高分子絮凝剂展示出优异的脱水性能。文中阐述了近年来用于污泥脱水的各类有机高分子絮凝剂及其在污泥脱水中的最新应用研究、污泥脱水方法和影响污泥脱水性能的因素。对絮凝剂的选择和污泥处理方法进行总结，得出：(1)选择阳离子性基团总数大于阴离子性基团总数的一种或多种絮凝剂；(2)采用先加入含有阳离子(或阳离子性)基团的无机(或有机)絮凝剂，然后加入分子量较高的有机高分子絮凝剂(两性型、阳离子型、非离子型或阴离子型)的污泥脱水方法。     

The effect of single and combined coagulation/flocculation methods on the sedimentation behavior and conductivity of bentonite suspensions with different swelling potentials

ABSTRACT

In this study, the sedimentation behavior of bentonite (Na and Ca bentonite) suspensions with different swelling potentials was investigated with single and combined coagulation and flocculation methods. The samples exhibited a negative surface charge over a broad pH range and had a relatively high suspension stability. Al₂(SO₄)₃, FeCl₃, MgCl₂, CaCl₂, and NaCl were used as coagulants. All coagulants have provided sedimentation efficiencies higher than 85% with Ca bentonite suspension, but only 22% efficiency was seen with Na bentonite suspensions. The effectiveness of coagulants increased with higher ionic values of the metal salts. Versus monovalent cations, multivalent cations had a greater influence on the zeta potential of the samples. Higher coagulant concentrations enhance the conductivities of the suspensions. In flocculation, anionic (A-150), cationic (C-521) and nonionic (N-100) flocculants were used. For a Ca bentonite suspension, all flocculants have 98% efficiency. The anionic flocculant was more efficient than cationic and nonionic ones for Na bentonite suspension. The dual-flocculation of cationic and anionic flocculant combinations and pre-destabilization via coagulants of Na bentonite suspension were also studied. Better flocculation performance was achieved with these combined methods.     

An evaluation of machine learning and artificial intelligence models for predicting the flotation behavior of fine high-ash coal

In this study, five different machine learning (ML) and artificial intelligence (AI) models: random forest (RF), artificial neural networks (ANN), the adaptive neuro-fuzzy inference system (ANFIS), Mamdani fuzzy logic (MFL) and a hybrid neural fuzzy inference system (HyFIS) were employed to predict the flotation behavior of fine high ash coal in the presence of a novel “hybrid” ash depressant consisting of polyacrylamide chains grafted onto aluminium hydroxide nanoparticles: Al(OH)₃-PAM (Al-PAM). A total of 51 flotation tests were conducted on coal samples with 38% ash-content and a P₈₀ of approximately 49?μm. Different influencing variables of coal flotation including polymer dosage, pH, polymer conditioning time, sodium metasilicate dosage (commercial dispersant), and the impeller speed were used as inputs for the models. The combustible recovery and ash content of coal reported to the concentrate were used as response variables (outputs). For AI model development, 80% of the total data was used for training phase and 20% was used for testing phase. Coefficient of determination (R²) and root-mean-square error (RMSE) were used as performance indicators of the models. The MFL model showed the best accuracy for the prediction of the combustible recoveries and the froth ash contents for this specific feed. However, in case of any significant change in the characteristics of the feed, these models would have to be re-trained using the data obtained through further physical experimentation and/or process model simulations. Moreover as these models are trained on laboratory scale data, these are only good for the predictions at laboratory scale.     

Chemically enhanced filtration and dewatering of narrow-sized coal particles

An experimental study of the filtration and dewatering of fine coal with and without additives was carried out. Filtration and dewatering behavior were determined using a vacuum filtration cell. The variables studied included the driving force, solids concentration, filter area, particle size and slurry pH. The effects of several flocculants, surfactants and hydrophobing additives (oils) on final moisture content of the filter cakes were determined. The investigations included determination of the rates of filtration and dewatering, assessment of the effects of additive type (anionic, cationic and nonionic), and establishment of optimum dosage of additives. Overall, it was found that the filtration and dewatering behavior were enhanced by increased driving force, higher initial slurry concentration, larger filtration area, larger particle size and lower slurry pH. Among surfactants and flocculating additives the anionic types were found to do the best job of filtration enhancement. At optimum dosages, the final cake moisture contents were reduced by 3.6% and 5.8% by weight using the appropriate surfactant and flocculant, respectively. However, the best filtration enhancements were achieved by addition of oils, which yielded cake moisture reductions of approximately 10% by weight.     

一水硬铝石型高硫铝土矿脱硫研究进展

一水硬铝石型高硫铝土矿脱硫成为解决我国优质铝土矿资源短缺的热点问题。对前人研究的高硫矿成分、物相、形貌进行了总结,全面阐述了拜耳法生产氧化铝过程中硫、铁的行为和危害,详细介绍了国内外研究脱硫的机理、方法及其效果。提出"三步走战略",即先浮选,后氧化,再沉淀三道工序进行脱硫,且对高硫铝土矿中所含不同成分的硫应采用不同方法脱硫。对含黄铁矿最高的高硫铝土矿可以通过先进行浮选工艺,再对含黄铁矿较高的铝土矿精矿在溶出过程中氧化S2-和溶出后在铝酸钠溶液中添加钡盐沉淀SO_4~(2-)的方法协同达到脱硫的目的。最后展望了高硫铝土矿脱硫未来的研究方向。     

Optimization of reagent dosages with the use of response surface methodology and evaluation of test results with upgrading curves in graphite flotation

The aim of this study is to reduce reagent consumptions in graphite flotation with the addition of Aero 3477 promoter to the flotation stage. A three-level Box–Behnken design is used for optimization and modeling of flotation stages. For this purpose, the flotation experiments are performed in two steps. The maximum weight recovery and the minimum ash content values of the rougher concentrate are calculated as 21.41 and 32.49% using diesel oil dosage (714.24?g/t), methyl isobutyl carbinol (MIBC) dosage (212.81?g/t), and sodium silicate (Na₂SiO₃) dosage (1451.189?g/t), respectively, in the preliminary experiment tests. Subsequently, keeping the Na₂SiO₃ dosage constant, Aero 3477 promoter is added to the flotation stage to provide reduction at reagent consumptions. As a result, the reagent consumptions of diesel oil dosage (162.10?g/t), MIBC dosage (129.58?g/t), and Aero 3477 promoter dosage (168.96?g/t) are supplied to reach the approximate weight recovery and the ash content as in primary experimental results. Considerable dosage decreases in both diesel oil and MIBC are achieved using promoter. Moreover, experimental studies are also evaluated using upgrading curves.     

Biobased polymeric flocculants for industrial effluent treatment

Water is a scare commodity now. Recycling of municipal wastewater, industrial and mineral processing effluents require treatment with the inorganic or organic flocculants. Inorganic flocculants are used in large quantities, leave large amount of sludge and are very much affected by pH changes. Other polymeric flocculants are used in a very minute quantity, form large cohesive floc and are inert to pH changes. Both natural and synthetic polymers are used as flocculants. Natural polymers are biodegradable and are effective at very large dosages but are very shear stable. The synthetic polymers are highly effective flocculants at very small dosages and have high tailorability, but have poor shear stability. In the authors laboratory, a new class of flocculants has been developed by grafting polyacrylamide branches onto polysaccharide such as guargum, hydroxypropyl guargum, starch, amylopectin and sodium alginate. These grafted polysaccharides exhibit synergistic flocculation characteristics, shear stability and controlled biodegradability. Out of all the grafted polysaccharides, amylopectin grafted polysaccharides out performs most of the commercially available flocculants. The polacrylamide branches grafted on high molecular weight branched amylopectin have larger approachability to contaminants in the industrial effluents [1, 2].     

Beneficiation of a magnetite-apatite ore from Sung Valley,Shillong, Meghalaya

The beneficiation of apatite from low grade magnetite-apatite ore was studied. Wet magnetic separation followed by flotation was found effective. The effects of different grinds, pH, depressants and collectors at varying dosages were investigated. Various process parameters were optimized and the rougher concentrate was cleaned thrice for improvement in the apatite grade. Sodium silicate as depressant, sodium oleate as collector and pine oil as frother, at a pH of 7–7·5 (natural pH), for apatite flotation were found effective. The general flowsheet of the process was developed.     

Treatment of pulp and paper mill wastewater by polyacrylamide (PAM) in polymer induced flocculation

The flocculation performances of nine cationic and anionic polyacrylamides with different molecular weights and different charge densities in the treatment of pulp and paper mill wastewater have been studied. The experiments were carried out in jar tests with the polyacrylamide dosages range of 0.5-15 mg l(-1), rapid mixing at 200 rpm for 2 min, followed by slow mixing at 40 rpm for 15 min and settling time of 30 min. The effectiveness of the polyacrylamides was measured based on the reduction of turbidity, the removal of total suspended solids (TSS) and the reduction of chemical oxygen demand (COD). Cationic polyacrlyamide Organopol 5415 with very high molecular weight and low charge density is found to give the highest flocculation efficiency in the treatment of the paper mill wastewater. It can achieve 95% of turbidity reduction, 98% of TSS removal, 93% of COD reduction and sludge volume index (SVI) of 14 ml g(-1) at the optimum dosage of 5 mg l(-1). SVI values of less than 70 m lg(-1) are found for all polyacrylamide at their respective optimum dosage. Based on the cost evaluation, the use of the polyacrylamides is economically feasible to treat the pulp and paper mill wastewaters. This result suggests that single-polymer system can be used alone in the coagulation-flocculation process due to the efficiency of the polyacrylamide. Sedimentation of the sludge by gravity thickening with settling time of 30 min is possible based on the settling characteristics of the sludge produced by Organopol 5415 that can achieve 91% water recovery and 99% TSS removal after 30 min settling.     

Coagulation-flocculation as a pretreatment process at a landfill leachate nitrification-denitrification plant

The main aim of this research work was to study the possible application of coagulation-flocculation as a pretreatment process for young landfill leachate in order to prevent fouling in the ultrafiltration membranes employed for the separation of biomass in the biological plant. Jar-test experiments were carried out to determine the optimum conditions for the removal of turbidity colour and organic matter. The coagulants ferric chloride, aluminium sulphate and aluminium polychloride (PAX) were tested, along with different types of flocculants (anionic and cationic polyelectrolytes). Optimum pH values were around 4.0 and 6.0 for ferric chloride and aluminium sulphate, respectively. It was not necessary to alter the pH of the leachate when using PAX, as the optimum value was found to be similar to that of the leachate (around 8.3). Optimum dosages were 0.4 g Fe(3+)/L, 0.8 g Al(3+)/L and 4 g PAX/L, although there was not much difference in the results for lower dosage of PAX. The best results were found with this coagulant, obtaining 98% turbidity removal, 91% colour removal and 26% COD removal. When flocculants were also added, the results were similar to those found when adding only coagulants, although a considerable increase in the settling rate was obtained. The volume of the sludge generated represents around 4.5-5.0% when using ferric chloride or aluminium sulphate, and 15% when using aluminium polychloride.     

阴离子长链疏水缔合水溶性聚合物的合成及溶液性能

利用溶液聚合制备了离子型疏水缔合水溶性共聚物P(AM/AMPS/C11AM),在共聚物结构中引入了既带有疏水长链又带有可离子化的基团,红外光谱确认了所合成的共聚物为目标共聚物;P(AM/AMPS/C11AM)系列共聚物溶液的表观黏度与共聚物浓度有很大关系,即使在极低的共聚物溶液浓度下也具有很好的增粘效果;在一定温度,一定pH值和表面活性剂的条件下,研究了系列共聚物溶液行为,结果与接枝疏水单体改性的丙烯酰胺是不同的。荧光光谱研究证实了共聚物在水溶液中的缔合行为。     

The utilization of tamarind seed gum as a novel dolomite depressant in the selective flotation of apatite from dolomite

In this study, the separation of apatite from dolomite was first investigated by using tamarind seed gum (TSG) to depress the flotation of dolomite in sodium oleate (NaOL) collector system. The effects of pH and flotation reagents concentration were studied, and the results indicated that TSG could strongly depress the dolomite floatability rather than apatite floatability. A satisfactory separation effect was realized when pH was 9.0, TSG dosage was 10 mg/L and NaOL dosage was 40 mg/L, at which the recovery of single apatite and dolomite was 80.28 % and 3.46 % respectively, and the grade of P₂O₅ and the recovery of P₂O₅ of the concentrate was 35.86 % and 76 % respectively in mixed ore flotation experiments. To reveal the adsorption mechanism, the flotation reagents adsorption morphology, adsorption type, and adsorption site were analyzed through AFM images, zeta potential measurements, FT-IR spectra, and XPS spectra, respectively. It was found that TSG was adsorbed on apatite by hydrogen bond while adsorbed on dolomite by chemical bond. Hydrogen bond was weaker than chemical bond, thus NaOL could still express the strong adsorption on apatite surface when TSG was used as depressant, while TSG could impede NaOL to be adsorbed on dolomite. Therefore, TSG selectively restrained the flotation of dolomite, achieving the separation. Furthermore, the XPS results uncovered that the Ca and Mg of dolomite were the main active sites that react with TSG.     

The upgrading of rare earth oxides from iron-oxide silicate rich tailings: Flotation performance using sodium oleate and hydroxamic acid as collectors

To investigate the recovery of rare earth elements (REE) as a by-product from iron-oxide silicate rich tailings generated from the extraction of other primary commodities, bench scale flotation tests, in rougher-scavenger-cleaner configuration were studied. Preliminary mineralogical characterisation identified bastnäsite, monazite, stetindite, brannerite, florencite, and stillwellite as the REE minerals, with hematite and quartz being the major gangue minerals in the tailings material. The flotation response of the rare earth oxides (REO) and major gangue phases was investigated using sodium oleate and hydroxamic acid as collectors; and sodium silicate and starch as depressants. Generally, sodium oleate displayed relatively better selectivity for REO than hydroxamic acid in the presence of the depressants. The rougher-scavenger-cleaner flotation configuration using sodium oleate and the depressants produced a final concentrate recovering 63% REO at a grade of 2.25%. This investigation shows that both collectors may be used for REO recovery but the use of depressants is key, in tandem with cleaning of the rougher and scavenger concentrates. The pulp pH also had a strong impact on the flotation recovery of REO, with the selectivity deteriorating with increasing collector dosage. Furthermore, the high proportion of gangue minerals reporting to the concentrates, even with the use of depressants, affected the quality of concentrates grade. This study has shown that particle size distribution and mineralogical characteristics of feed significantly affect the upgrade and recovery of REO.     

A study on the modified flotation parameters and selectivity index in copper flotation

Selectivity index (SI) and modified flotation rate constants of copper and iron were evaluated to rougher flotation circuit of the Sarcheshmeh copper ore by a series of batch flotation tests. Kinetics model of Agar was fitted to experimental data. The results indicated that first-order kinetics model of Agar presented the time–cumulative recovery curves of flotation tests quite well for Cu and Fe. Also, the results showed that the selectivity between Cu and Fe enhanced with increasing the pH, solid content, and dosage collector. In addition, performance of collectors showed that the best selectivity between Cu and Fe was in the order of combination of Z11 and MBTs > flomin C4132 > combination of MBTs and flomin C4132 > combination of Z11, MBTs, and flomin C4132 in flotation of copper. It was also found that better results for flotation kinetics were obtained at pH 11.5, solid percentage 28, and dosage collector 40 g/t (15 g/t sodium isopropyl xanthate and 25 g/t mercaptobenzothiazole [MBT]). SI value was determined as 5.12 in optimum condition.     

In-line flocculation monitoring in a Hatschek machine for fibre–cement manufacture

The aim of this study is to obtain real-time information of flocculation processes in the fibre–cement manufacture through a soft sensor. This paper presents three different applied trials, carried out in different Hatschek machines, representing the main two industrial processes (air curing and autoclaving), in order to monitor the flocculant dosage changes, flocculant changes and the relationship between final product properties and flocculation. Three different anionic poly-acrylamides of low charge with different molecular weights were used as flocculants. The obtained results demonstrate that focused beam reflectance measurement (FBRM) is a valuable in-line sensor as well as a control and predictive process tool to monitor the flocculation processes in fibre–cement manufacture. Furthermore, a correlation between the sensor data (counts/s of particles between 50 and 86 μm) and the final product properties (density) was established, thus minimising the production of fibre–cement outside the intended specifications to achieve a better control on the final product quality.     

Analysis of reverse cationic iron ore fines flotation using RSM-D-optimal design – An approach towards sustainability

Froth flotation is an important process to recover iron values from slimes, ore fines to meet the rapidly growing demand of quality iron ore concentrate for environmental and economic advantages. In the present study, responses of ?75?µm iron ore fines to flotation were analysed at different variable parameters. The D-optimal design of response surface methodology was adopted to evaluate the effect of different reagents such as collector, frother, depressant, dispersant and pH on the recovery and grade. The RSM-D optimal predicted responses with the coefficient of determination (R²) 0.97 for recovery and 0.98 for grade of iron concentrate collected from tailing launder. The optimal conditions were collector?=?0.21?kg/ton, frother?=?0.10?kg/ton, depressant?=?0.61?kg/ton, disperssant?=?0.20?kg/ton, and pH?=?11 with 64.13% Fe and 84.37% iron recovery respectively with a model desirability of 84.3%. Flotation performance was optimized by carrying out statistical design of experiments to identify main and international effects on maximum recovery and grade. This study showed that RSM-D-optimal could efficiently be applied for modeling of iron ore reverse flotation and it is very economical to obtain maximum amount of information in less interval of time with few numbers of experiments. Successful upgradation of low-grade iron ore fines through reverse flotation route with proposed reagent regimes is envisaged.     

Influence of cationic flocculant properties on the flocculation of yeast suspensions

In this study four different cationic polyelectrolytes of different molecular weight and charge densities were used to flocculate yeast suspensions to determine the effect of flocculant dose, molecular weight and charge density on the resulting floc size, morphology and charge. The zeta potential of the negatively charged yeast flocs was observed to increase with flocculant dose. As the flocculant dose was increased the charge of the floc was observed to reverse; the actual dose at which charge reversal occurs being dependent on the flocculant charge density and molecular weight. Floc size and morphology, measured with a video camera, showed that higher molecular weight flocculants produced larger flocs for the same dose. The results obtained here suggest that that flocculants may be screened by determining the charge, size and morphology of the resulting floc particles which is less time-consuming.     

Novel application of depressant sodium mercaptoacetate in flotation separation of chalcopyrite and pyrite

The development of flotation reagents with high selectivity and strong depression ability is of great significance in the efficient enrichment of copper sulfide ores. In this work, a new depressant, sodium mercaptoacetate (SMA) has been explored for the flotation separation of chalcopyrite and pyrite, and the depression mechanism of SMA was studied by Fourier Transform Infrared spectrometer (FTIR), adsorption tests, local electrochemical impedance spectroscopy test (LEIS), Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). Micro-flotation tests showed that SMA strongly depresses pyrite in the pH range of 6–10. When the dosage of SMA is 2.5 × 10⁻⁵ mol/L, the dosage of SBX is 1 × 10⁻⁵ mol/L, and pH = 6.5, the concentrate with a Cu grade of 31.93% and chalcopyrite recovery of 85.97% can be obtained, in which the pyrite recovery was only 4.18%, respectively. The strong chemical adsorption between SMA and Fe atomic sites exposed on the surface of pyrite reduces the hydrophobicity of pyrite and hinders the adsorption of SBX. In comparison, SMA has less adsorption on the surface of chalcopyrite and hardly affects the further adsorption of SBX. It was shown that SMA could be used as an effective depressant for pyrite in the flotation separation of chalcopyrite and pyrite.     

壳聚糖/阳离子聚丙烯酰胺水分散聚合物的制备

以水溶性壳聚糖(Cts)作为新型分散剂,甲基丙烯酰氧乙基三甲基氯化铵(DMC)和丙烯酰胺(AM)为单体原料,偶氮二异丁基脒二盐酸盐(V-50)为引发剂,采用水分散聚合技术合成了壳聚糖/阳离子聚丙烯酰胺聚合物(Cts/CPAM),探讨了反应条件对聚合物分子量的影响。结果发现,单体质量分数为3.75%~4.25%、AM∶DMC(质量比)为9∶4、分散剂质量分数为1.5%~1.75%、无机盐质量分数为10.0%~17.5%、引发剂质量分数为0.0035%~0.0045%、反应温度为55℃~60℃时,分散聚合体系稳定,所制备聚合物的分子量较高。     

含氟丙烯酸酯复合乳液的制备及性能

含氟丙烯酸酯性能优异,目前以丙烯酸六氟丁酯(HFBM)单体合成水性含氟丙烯酸酯乳液的报道较少。以甲基丙烯酸甲酯(MMA)、丙烯酸丁酯(BA)、丙烯酸(AA)为主要单体,HFBM为功能单体,采用预乳化工艺合成了含氟丙烯酸酯复合乳液,优化了乳液合成条件(复合乳化剂配比、引发剂用量、含氟单体用量),并用红外光谱和热重分析研究了优化条件合成乳液的结构和其所成乳胶膜的热稳定性。结果表明:复合乳化剂中m(十二烷基硫酸钠)∶m(曲拉通X-100)=3∶2,引发剂(过硫酸钾)用量为1.0%,含氟单体用量为9%时,合成的含氟丙烯酸酯复合乳液性能最好,具有较大的单体转化率和较小的凝胶率,乳胶膜有较大的拉伸强度;HFBM被成功地引入聚合物链段结构中,并使聚合物的热稳定性大幅提高。