Studied sludge samples are composed of major goethite and quartz; less clay minerals; and minor magnetite, hematite, clinochlore and todorokite. They have quite similar qualitative, but different semi-quantitative compositions. There are similar particle size distributions between the samples, and the highest contents of ~50% belongs to the finest classes of <6 μm. Among size classes within the samples, almost identical iron contents are present; indicating their similar mineral compositions, which make these systems very complex for further separation processes. Sludge II has a higher natural settling rate, due to its higher density and mineral composition. With addition of the flocculant, settling rates increase significantly with the increase of the liquid component in both of the samples. The effect of flocculant on the settling rate is different between samples, and depends on their mineral composition. The time of settling does not play a role in selectivity, to the ratio of the mass of floating and sinking parts, and iron content does not change with time. The content of iron partially increases by flocculation; therefore, this method should be considered as an appropriate one. Zeta potential values for sludge are mostly between those for goethite and quartz, indicating their particle mixture and intricately association.

Constanta port operations involving the handling of bulk minerals often lead to material losses, resulting in mineral waste, containing a mixture of iron ore, bauxite, and coal, amongst others. In order to recover these minerals, a processing plant was built, which successfully separates most of this waste into its constituents. However, a byproduct obtained from this process is a sludge containing fine particles below 0.5 mm, which are deposited in a reservoir that represents definitive tailings. Since this is a “rich” tailing material, which is difficult to be extracted by using conventional methods due to its small size, the selective flocculation procedure was tested as an alternative method. This paper presents the results obtained for standard methods of selective flocculation tests using polyacrylamide A 100 at a pH value of 10.5. SEM-EDS and XRD analyses were performed, and the chemical composition of the sample components was given. According to preliminary tests, using the selective flocculation procedure, the expected results were obtained in terms of separating the overflow between the content of impurities (with a reduced share of Fe in relation to the input) and sediment with an increased content of Fe (with a reduced share of impurities in relation to the entrance).

The paper represents a part of research conducted with the aim of examining the possibility of applying selective flocculation of goethite from sludge that occurs in the process of iron ore production. The aim of this study was to compare the influence of polyacrylamide and sodium oleate as a flocculant on the settling behavior of goethite under different conditions. The paper presents the results of the research on the influence of the flocculants based on polyacrylamide and sodium oleate, as well as pH values on the settling rate of a natural goethite sample. The results showed that the settling rate of goethite was influenced by pH value and the type of flocculant, while the concentration of flocculant did not significantly affect the settling rate. Measurements of zeta potential showed the effect of flocculants on the surface of the goethite.

Elevated salinity can significantly affect the rheological behavior, thickening time, and early strength development of API Class G cement slurries. This study experimentally investigated the effect of NaCl additions of 0, 4, and 8 wt.% BWOC on cement slurries with densities of 1.5 and 1.9 g/cm³ at temperatures of 25, 50, 75, and 90 °C. Rheological parameters, the time required to reach a consistency of 30 Bc under atmospheric pressure, the times required to attain selected compressive strength thresholds, and the ultrasonic cement analyzer (UCA)-estimated compressive strength after 12 and 24 h were evaluated.The results demonstrated that the effect of NaCl was not pro-portional to its concentration but depended on slurry density, temperature, and the property being evaluated. NaCl generally reduced plastic viscosity and yield stress, whereas gel strength exhibited a non-uniform response with a pronounced dependence on temperature. Its influence on thickening time and early strength development was likewise non-monotonic. Under certain test conditions, higher NaCl concentrations accelerated the attainment of the initial strength thresholds; however, they did not consistently increase the UCA-estimated compressive strength after 24 h or improve all evaluated operational properties. Among the investigated salinity levels, the slurry containing 4 wt.% NaCl exhibited the most balanced overall performance in terms of rheological behavior, thickening time, and early mechanical properties across both slurry densities and the investigated temperature range. Nevertheless, this concentration did not provide the best performance for every individual parameter or under all test conditions. The findings provide a basis for the further op-timization of cement slurry formulations intended for use in high-salinity environments. Since the experimental program did not include independent repetitions, the observed differences should be interpreted as descriptive trends that require statistical validation in future studies.

Elevated salinity can significantly affect the rheological behavior, consistency development, and early strength development of API Class G cement slurries. This study experimentally investigated the effect of NaCl additions of 0, 4, and 8 wt.% BWOC on cement slurries with densities of 1.5 and 1.9 g/cm³ at temperatures of 25, 50, 75, and 90 °C. Rheological parameters, the times required to attain selected UCA-estimated compressive strength thresholds, and the ultrasonic cement analyzer (UCA)-estimated compressive strength after 12 and 24 h were evaluated. The results indicated that the effect of NaCl was not proportional to its concentration but varied with temperature, slurry formulation, and the property being evaluated. NaCl generally reduced plastic viscosity and yield stress, whereas gel strength exhibited a non-uniform response with a pronounced dependence on temperature. Its influence on atmospheric consistency development and early strength development was likewise non-monotonic. Under certain test conditions, higher NaCl concentrations accelerated the attainment of the initial strength thresholds; however, they did not consistently increase the UCA-estimated compressive strength after 24 h or improve all evaluated operational properties. Among the three investigated NaCl concentrations, the 4 wt.% formulation frequently exhibited favorable responses across several evaluated parameters; however, no single NaCl concentration consistently provided the most favorable response for every property or under all investigated conditions. The findings provide a basis for the further optimization of cement slurry formulations intended for use in high-salinity environments. Since the experimental program did not include independent repetitions, the observed differences should be interpreted as descriptive trends that require statistical validation in future studies.