Polymer adsorption: its correlation with flocculation and dewatering of kaolin suspension in the presence and absence of surfactants

Characterization of structure-function properties relevant to copper-activated pyrite depression by different starches

Starches can adsorb on and depress copper-activated pyrite desirably during flotation, an important process in ore mineral extraction. In order to develop structure/function relationships, adsorption on and depression properties of copper-activated pyrite at pH 9 by normal wheat starch (NWS) and high-amylose wheat starch (HAW), dextrin, and a range of oxidized normal wheat starches (peroxide and hypochlorite treated) were investigated. Adsorption isotherms and bench flotation performance were compared with kinematic viscosity, molar mass distribution, surface coverage, and substituted functional groups assay. The differences in molar mass distribution and substituted functional groups among oxidized starches had little influence on the depression of copper-activated pyrite. However, the introduction of -C=O and -COOH substituents, combined with depolymerization, improved solubility and dispersibility, reduced aggregated structures, and strengthened surface binding of oxidized polymers, compared with NWS and HAW. At high concentrations, HAW, NWS, and dextrin were adsorbed onto the pyrite surface more than oxidized starches. However, at the low concentrations of depressant used in flotation, oxidized starches were more effective at selectively masking copper sites. This study suggests that a stable chelation between Cu(I) and starch ligands is necessary for depression of copper-activated pyrite at pH 9, which can be achieved with oxidized wheat starch.

Flocculation and dewatering of the Kaolin slurry treated by single- and dual-polymer flocculants

To mitigate the sudden increase in the production of waste engineering slurry, predominantly composed of Kaolinite, this study investigated the flocculation and dewatering of Kaolin slurry treated with single- and dual-polymer flocculants. The influence of the flocculant type and dosage, under single- and dual-dose conditions, on slurry's sedimentation and the filtration characteristics, were thoroughly discussed. The results reveal that the adsorption bridging of the polymeric flocculant, resulting from hydrogen bonds, exerts a more significant effect than electrical neutralization on forming a large floc. Under single-dose conditions, nonionic polyacrylamides (NPAMs) with the strongest adsorption bridging leads to biggest flocs and the maximum settling rate of 21.55 mm/s. Under the dual-dose conditions of polymeric aluminium chloride (PAC) and PAM, the size of the slurry's floc decreases with an increase in PAC dosage. Nevertheless, the filtration performance of the slurry improves, with the lowest SRF value of the flocculated slurry being 1.58 × 10¹¹ m/kg as 3‰ PAC and 3‰ NPAM is dosed. The improvement is explained by the micro-pore distribution of sludge. According to Mercury intrusion porosimetry (MIP) test, the slurry treated with the optimal dosage of dual-polymer flocculant exhibits the greatest sludge pore size and connected porosity (with a maximum value of 20.99%). Furthermore, the study discusses and compares the flocculation mechanism of single- and dual-polymer flocculants. The obtained results provide guidance for selecting appropriate flocculants for dewatering inorganic slurries, using different dewatering methods, such as gravitational thickening or filter pressing.

Adsorption behaviour of hydrogarnet for humic acid

Discharge of humic acid (HA) in aqueous environments is a key health and aesthetic issue. The present work investigates the use of hydrogarnet as a novel adsorbent for HA. Hydrogarnet was hydrothermally synthesized with different solvents to control the chemical composition. Hydrogarnet with three types of chemical compositions had better adsorption properties for HA than hydrogarnet with a single chemical composition. Controlling the chemical composition of hydrogarnet increased the number of hydroxyl groups and the overall binding energy of the system, leading to changes in the zeta potential. The enhancement of these adsorption properties is related to the increased numbers of hydroxyl groups on the surface and their diverse binding energies.

Formation of cationic hydrophobic micro-blocks in P(AM-DMC) by template assembly: characterization and application in sludge dewatering

The existence of template did play a role of molecular assembly in the radical polymerization, and the cationic hydrophobic micro-blocks in the polymer slightly improved the sludge dehydration performance.

Effects of surfactants on the improvement of sludge dewaterability using cationic flocculants

The effects of the cationic surfactant (cationic cetyl trimethyl ammonium bromide, CTAB) on the improvement of the sludge dewaterability using the cationic flocculant (cationic polyacrylamide, CPAM) were analyzed. Residual turbidity of supernatant, dry solid (DS) content, extracellular polymeric substances (EPS), specific resistance to filtration (SRF), zeta potential, floc size, and settling rate were investigated, respectively. The result showed that the CTAB positively affected the sludge conditioning and dewatering. Compared to not using surfactant, the DS and the settling rate increased by 8%–21.2% and 9.2%–15.1%, respectively, at 40 mg·L⁻¹ CPAM, 10×10⁻³ mg·L⁻¹ CTAB, and pH 3. The residual turbidities of the supernatant and SRF were reduced by 14.6%–31.1% and 6.9%–7.8% compared with turbidities and SRF without surfactant. Furthermore, the release of sludge EPS, the increases in size of the sludge flocs, and the sludge settling rate were found to be the main reasons for the CTAB improvement of sludge dewatering performance.

Polymer flocculation mechanism in animal slurry established by charge neutralization

Flocculation and filtration of animal manure is practically and environmentally beneficial. However, the flocculation mechanism in manure need to be clarified to use the technique efficiently rather than relying on trial-and-error. Manures were flocculated with polyacrylamides. Floc size, dewaterability, dry matter and turbidity were measured. At optimal polymer volume, the charge neutralization was determined, i.e. amount of negative manure particle charge neutralized by positive polymer charge. The optimal cationic polymer properties were linear and very high molecular weight, which caused efficient particle catching. And it had medium charge density, which caused efficient particle attachment. The required charge neutralization was 5-23% (15% for the optimal polymer). Polymer bridging proved the dominant flocculation mechanism; patch flocculation may be slightly significant for some polymers, while coagulation proved insignificant. Manure's high ionic strength, high dry matter content and highly charged small molecules caused bridging to be more dominant in manure than in other typically flocculated media.

Kinetics and adsorption behavior of carboxymethyl starch on α-alumina in aqueous medium

The adsorption of carboxymethyl starch (CMS) at the alpha-alumina/aqueous solution interface has been investigated through adsorption studies, electrokinetics mobility measurements, and FTIR spectroscopy. Zeta potential measurements show that the addition of CMS results in a more dramatic increase in the absolute zeta potential in the alkaline region, as well as a shift of the isoelectric point to lower values, indicating the adsorption of CMS from the aqueous solution onto the alumina surface. The positive hydrophilic surface sites of alumina are responsible for the adsorption of CMS molecules. The adsorption of CMS is possible after charge reversal by the addition of excess CMS. Nearly 30 min of contact time are found to be sufficient for the adsorption of CMS to reach equilibrium. CMS adsorption follows a Langmuir isotherm with adsorption capacities of 91.74 mg CMS per gram of alpha-alumina. For the adsorption of CMS, pseudo-second-order chemical reaction kinetics provides the best correlation with the experimental data. FTIR analysis indicated that CMS forms outer complexes with alumina surfaces depending on the shifting of the asymmetric and symmetric bands.