Journal Of Iranian Water Engineering Research

Journal Of Iranian Water Engineering Research

The effect of adding sodium hydroxide on increasing the speed of water recovery in settling ponds of sand processing companies

Document Type : Research Article

Author
tabriz university-iran
10.22034/ijwer.2026.552397.1113
Abstract
Water recovery is now more crucial than ever because of the ongoing water crisis. Water extracted from the auger is held in settling ponds for a few days in order to prepare pure water and restore it into the production cycle in sand and gravel industries. Significant water savings can be achieved by shortening the settling period, which allows the water from the settling ponds to be restored to the production line more quickly. Companies that use a lot of water include those that produce sand. To allow the mud and silt to settle and allow the pure water to return to the production cycle, the water discharged from the auger in these complexes is moved to settling ponds and held there for a number of days. The most popular water recycling feature in sand businesses is settling ponds. This approach has a huge capacity and is reasonably priced. A layer of pure water forms in the ponds top sections as a result of suspended particles and solid grains settling. It should be emphasized that in these ponds, settlement is done using solely gravity. Using gravity is one of the common methods for settling suspended particles from water. The mining and chemical industries are the primary users of this technique. Gravitational sedimentation is most effective when there is a significant density differential between solids and liquids. This primarily pertains to situations in which water is utilized as the liquid. Newton's and Stokes' laws can be used to determine the settling velocity of solid particles in settling ponds. Micron-sized particles have a slow settling velocity because of gravity; under certain situations, centrifugal force can be used to accelerate their dropping velocity. It is also possible to modify the environment to cause the particles to coagulate, settle more rapidly, and adhere to one another by the Ney van der Waals effect. This process, known as flocculation, can also be accomplished with a variety of flocculents. In sand washing operations, the coagulation and settling process in settling ponds is crucial. The settling velocity can be raised by using flocculating agents. The purpose of flocculating agents is to destabilize and bind together charged suspended particles. In addition to flocculants, which can neutralize and precipitate suspended particles in water, suspended particles in water can have a positive, negative, or uncharged electrical charge. In the settling ponds of Roshan Ghadam Sand Company, the impact of adding sodium hydroxide solution—a by-product of Chloropars Tabriz Company—on shortening the muds settling time was examined. Measurements revealed that the time needed for the mud line to stabilize decreased from 78 minutes to 33 minutes when the concentration of sodium hydroxide was increased from 0.5 vol.% to 3.5vol.%. Coagulation, flocculation, or a mix of the two processes initiate the aggregation of mud particles. The addition of sodium hydroxide alters the surface charge of clay particles, which are negatively charged. The coagulation process starts when the clay particles approach one another due to a change in their surface charge. Areas with opposing charges are used in this technique.The clumps aggregate more when the amount of flocculant increases, and the clumps created from the coagulated clumps are stronger when there is more flocculant present. Under these circumstances, flocculation results in the formation of larger clumps. In kaolin pulps, clay clumps have an edge-plate structure at low pH and a plate-plate structure at high pH. This idea states that the presence of positively charged sites—Na-OH at the edges in contact with negatively charged surfaces—is what causes the edge-surface structure. Low ionic strength may result in the edge-edge contact state when the boundary at the edge surface is the isoelectric point. The settling rate is significantly influenced by the size of the clumps that form. An electric double layer forms surrounding each suspended particle as a result of the electrostatic attraction between the clay particles in water and the oppositely charged ions of the flocculant solution. Forces are created between clay particles suspended in solution as a result of the interaction of double layers surrounding them. Because to isomorphic replacements, the surface of kaolin particles in water is permanently negatively charged. For instance, trivalent cations Al^(3+)or Fe^(3+)could take the place of Si^(4+) in the sheet. Additionally, divalent cations like Mg^(2+)or Fe^(2+) could take the place of Al^(3+). A charge deficit and a negative potential are produced at the base surface if these replacements take place. Different amounts of sodium hydroxide flocculant were added to various solutions in order to assess their pH. The pH of the solution rose as the amount of sodium hydroxide increased. It should be mentioned that the pH of the solution rose to 8 when 3.5 vol.% of sodium hydroxide was added. Therefore, it may be concluded that increasing the sodium hydroxide concentration in this system is risky. Because of the elevated pH, adding more sodium hydroxide to the settling pond water can accelerate the corrosion of the equipment's metal components. Therefore, in the settling ponds of Roshan Ghadam Sand Company, the maximum amount of sodium hydroxide flocculant utilized to boost the settling rate is 3.5 vol.%.
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