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• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
  • B01J20/06—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising oxides or hydroxides of metals not provided for in group B01J20/04
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/30—Processes for preparing, regenerating, or reactivating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/30—Processes for preparing, regenerating, or reactivating
  • B01J20/3028—Granulating, agglomerating or aggregating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/30—Processes for preparing, regenerating, or reactivating
  • B01J20/3085—Chemical treatments not covered by groups B01J20/3007 - B01J20/3078
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J41/00—Anion exchange; Use of material as anion exchangers; Treatment of material for improving the anion exchange properties
  • B01J41/08—Use of material as anion exchangers; Treatment of material for improving the anion exchange properties
  • B01J41/10—Inorganic material
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G19/00—Compounds of tin
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G19/00—Compounds of tin
  • C01G19/02—Oxides
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G37/00—Compounds of chromium
  • C01G37/02—Oxides or hydrates thereof
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/28—Treatment of water, waste water, or sewage by sorption
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/28—Treatment of water, waste water, or sewage by sorption
  • C02F1/281—Treatment of water, waste water, or sewage by sorption using inorganic sorbents
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/60—Compounds characterised by their crystallite size
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/10—Inorganic compounds
  • C02F2101/20—Heavy metals or heavy metal compounds
  • C02F2101/22—Chromium or chromium compounds, e.g. chromates
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
  • C02F2103/02—Non-contaminated water, e.g. for industrial water supply
  • C02F2103/023—Water in cooling circuits
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
  • C02F2103/16—Nature of the water, waste water, sewage or sludge to be treated from metallurgical processes, i.e. from the production, refining or treatment of metals, e.g. galvanic wastes
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
  • C02F2103/22—Nature of the water, waste water, sewage or sludge to be treated from the processing of animals, e.g. poultry, fish, or parts thereof
  • C02F2103/24—Nature of the water, waste water, sewage or sludge to be treated from the processing of animals, e.g. poultry, fish, or parts thereof from tanneries
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2305/00—Use of specific compounds during water treatment
  • C02F2305/08—Nanoparticles or nanotubes

Definitions

• the invention belongs to the field of chemical engineering and specifically to the water purification technology using solid adsorbents.
• Solid adsorbents are applied by the current state of the art as filling media in column beds for the removal from water and wastewater of oxidative ions like bromates, chlorates, perchlorates, as well as chromates (hexavalent chromium) from drinking water or wastewater by adsorption.
• chromium in water may be attributed to anthropogenic (tannery, plating, cooling towers, etc.) or natural origin with the latter explained by its release during water contact with alluvial precipitates formed by the erosion and weathering of ultramafic rocks. Since Cr(lll) solubility in the common pH range of drinking water (6.5-8.5) is estimated lower than 5 ⁇ g L, higher concentrations of dissolved chromium in natural water should be related to the presence of the more soluble Cr(VI) form.
• Cr(VI) Due to its high toxicity and the confirmation of its natural formation in groundwater, Cr(VI) is considered as a priority pollutant by the World Health Organization.
• MCL maximum contaminant level
• E.U. 50 ⁇ ig/L.
• Such legislation for total chromium instead of its specification for Cr(VI) arises by the initial consideration that the presence of Cr(VI) in the environment is solely caused by anthropogenic activities. Nevertheless, recent studies indicate natural procedures as the main source of water pollution by chromium and that the Cr(VI) is the dominant form (N. Kazakis et al., Sci. Total Environ. 514 (2015) 224, E.
• adsorption is the optimum method for Cr(VI) removal since it does not only comply with these criteria but it also provides flexibility in the design and operation of the process.
• adsorbents like biological material, inorganic oxides, activated carbon and others are attracting the interest of researchers.
• Activated carbons are the most widely used adsorbents for water and wastewater treatment. Particularly, they are promoted due to their high specific surface area and their wide availability in market.
• the main mechanism of Cr(VI) removal is considered to be the surface reduction followed by the adsorption as Cr(lll) (D. Mohan, C.U. Pittman Jr., J. Hazard. Mat, B137 (2006) 762).
• bio-adsorbents bacteria, algae, fungi
• drawbacks also stand for bio-adsorbents (bacteria, algae, fungi), which additionally demand large contact times to maximize their activity.
• bio-adsorbents cause deterioration in the quality of drinking water as a result of its enrichment by organic compounds and microorganisms.
• Metals and metal oxides that can act as electron donors appear advantageous due to their ability to reduce Cr(VI) to insoluble Cr(lll) hydroxides, which are then retained onto their surface. In that way operate zero-valent iron, magnetite (FeaC ), copper, zinc, magnesium and alloys (e.g. zinc-copper).
• FeaC magnetite
• copper, zinc, magnesium and alloys e.g. zinc-copper
• SnCl2-2H20 is hydrolyzed by 1 N NaOH (0.4 g are dissolved in 10 mL of distilled water), that is, at a strongly alkaline environment.
• 1 N NaOH 0.4 g are dissolved in 10 mL of distilled water
• synthesis under high pH values leads to the formation of oxides.
• SnO bivalent tin oxide
• the reaction takes place under heating, which diminishes the concentration of dissolved oxygen and in this way limits oxidation to Sn02.
• Sn604(OH) 4 as an intermediate step before SnO production is something that is merely assumed in said document but not proved therein though , wherein it is stated that «With the increasing of SnCh-2H20 amount, the solution turned to ivory-white suspension, and then to light yellow suspension indicating the formation of Sne04(OH)4.
• the layer ablation liquid phase method is a production method of high energy demands, taking place in batch mode, in a quartz cell where the laser beam is directed to and it requires tin of high purity (99.99 %). It is a quite good method to produce materials of high quality and accurate morphology, but only for quantities of few milligrams up to some grams, which are considered very small for environmental applications with demands of thousands of tons.
• this document discloses a batch mode synthesis method for bivalent tin oxy-hydroxides, with low production rate and high energy demands, implying a huge production cost and a non-acceptable water treatment cost. Furthermore, it is obvious that the synthesis conditions cannot cover in a large-scale the requirements of the use mentioned in the latter document (photocatalytic oxidation of methyl red) independently from the treatment cost. Conclusively, the synthesis conditions are not focused in the optimization of the surface charge so as to achieve an at least acceptable removal efficiency for hexavalent chromium.
• an adsorbent consisting of bivalent tin oxy-hydroxide of the type Sn x O y (OH)z, with 1 ⁇ x ⁇ 6, 0 ⁇ y ⁇ 4 and 0 ⁇ z ⁇ 4, taking place in the pH range 2-12 and followed by a thickening and drying process.
• the aim of this invention is the preparation of an adsorbent which combines reducing and adsorbing properties achieving a high Cr(VI) removal efficiency from water.
• Such properties are accomplished by the hydrolysis of Sn(ll) salts in a two-stage continuous flow reactor where pH is adjusted to the targeted point by the addition of an alkaline solution.
• the present invention faces the problem of Cr(VI) removal from water in the following way, thereby providing a suitable solution to it.
• the adsorbent successively reduces Cr(VI) to Cr(lll), since it shows reducing potential without passivation problems, and then captures Cr(lll) in the structural unit of the oxide/oxy-hydroxide. More specifically, during contact with polluted water, Cr(VI) is initially adsorbed on the surface of Sn60 4 (OH) 4 and then, the reduction of Cr(VI) takes place following reaction [2]:
• the invention provides a method for the synthesis of bivalent tin oxy-hydroxide with chemical formula Sn60 4 (OH) 4 under acidic environment (pH ⁇ 4) in a continuous-flow reactor.
• the main feature of the method is the stabilization of the crystal structure Sn60 4 (OH) 4 against oxidation or dehydroxylation combined with the development of a dense positive charge on its surface.
• the synthesis of positively- charged Sn60 4 (OH) 4 differentiates the method according to the invention from any other method producing the same phase, but with much different physical properties and technological features.
• the method according to the invention has an additional important advantage: the high stability of the structure Sn60 4 (OH) 4 against oxidation effects or transformation to oxides (Sn0 2 ) with very limited removal efficiency for hexavalent chromium.
• the low efficiency of Sn02 is observed in the corresponding breakthrough curve of Figure 8.
• the specific advantage is also attributed to the acidic conditions of synthesis reaction as analysed below.
• the oxidation of bivalent tin is a spontaneous process due to the presence of dissolved oxygen in water. Under acidic environment, the oxidation reaction of Sn 2+ with the simultaneous reduction of oxygen is described by the following electrochemical equations:
• thermodynamic equilibrium phase diagram of tin in water represented in Figure 9 as a function of the pH value and the redox potential.
• the remarkable distinctive contribution of the method according to the invention is based on the fact that the synthesis reaction of the material takes place under a constant pH value between 2 and 4 and the control of redox potential at a constant value in the range from 0 to 0.3 V, respectively, following a continuous-flow two- stage process.
• the already known Sn60 4 (OH) 4 phase is formed, but with characteristics that are completely different from the material prepared by the known chemical precipitation methods of the current state of the art.
• the bivalent tin oxy- hydroxide Sn60 4 (OH) 4 of the method according to the invention should be considered as a distinctive chemical compound, although it is synthesized by a modification of a common reaction, due to the high chemical stability and the excess of positive surface charge preserved.
• Figure 1 is a diagrammatic representation of the chemical reaction involved in the method according to the invention.
• Figure 2 shows a simplified flow diagram of the synthesis procedure for the adsorbent according to the method of the invention.
• Figure 3 shows an X-ray diffraction diagram of the material prepared according to the procedure given in Example 1 of method's application, verifying the existence of one bivalent tin oxy-hydroxide phase with the structure Sn604(OH)4.
• Figure 4 similarly shows an X-ray diffraction diagram of the material prepared according to the procedure given in Example 2 of the method's application, verifying the existence of one bivalent tin oxide phase with the structure SnO.
• Figure 5 further shows an X-ray diffraction diagram of the material prepared according to the procedure given in Example 4 of the method's application, verifying the existence of a major bivalent tin oxy-hydroxide phase with the structure Sn604(OH)4 and a small contribution by a bivalent tin oxide phase with the structure SnO.
• Figure 6 shows breakthrough curves of laboratory rapid small scale column tests for Cr(VI) adsorption test from Sn604(OH)4 adsorbent synthesized at pH 9, which illustrates the low influence of adsorption pH values in the range 7 - 8 commonly encountered in drinking water.
• Initial concentration 100 ⁇ sg Cr(VI)/L, empty bed contact time 2 min, grains sized 0.25-0.5 mm and temperature 20 ⁇ 1°C.
• Figure 7 is a representation of a curve showing the effect of synthesis conditions (pH) of Sn60 4 (OH)4 in the positive surface charge density.
• Figure 8 shows a set of breakthrough curves for Cr(VI) in rapid small scale tests for Sn604(OH)4/Sn02 samples synthesized under various pH values and a corresponding Sn02 sample.
• Initial concentration 100 g Cr(VI)/L, water pH 7.1 ⁇ 0.1 , empty bed contact time 4 min, grains sized 0.25-0.5 mm and temperature 20 ⁇ 1°C.
• Figure 9 shows a thermodynamic equilibrium phase diagram of tin in water as a function of the pH value and the redox potential.
• a synthesis method of the adsorbent [Sn x Oy(OH) z ], with 1 ⁇ x ⁇ 6, 0 ⁇ y ⁇ 4 and 0 ⁇ z ⁇ 4, is performed as follows: a continuous flow and stirred reactor is used consisting of two stages (1) and (2) in each of which the retention time is at least 30 min as shown in Figure 2. An aqueous solution of SnSCU or SnC or Sn(N03)2 with concentration 1-100 g/L is continuously fed in the reactor 1 with a flowrate Q. The hydrolysis/precipitation reaction of bivalent tin takes place mainly in reactor 1 under intense stirring. Reactor 1 is connected to reactor 2 where the reaction is finalized under mild stirring conditions.
• the quantity of the product is defined by the flowrate and concentration of Sn(ll) salt solution.
• pH value is adjusted throughout the reaction duration at a constant point in the range 2-12 the addition of one or a combination of more than one of alkaline reagents NaOH, NaHCC-3, Na2C03, KOH, KHCO3, K2CO3, Ca(OH) 2 .
• the outflow from reactor 2 is collected in a thickening tank 3 under mild stirring for a period of 1-48 h to stabilize the nano-crystalline geometry of the material and a size in the range of 20-50 nm, e.g.
• nanocrystal size is around 45 nm for the material prepared according to Example 1 of method's application and around 20 nm for the material prepared according to Example 2 of method's application.
• the precipitate after thickening is mechanically dewatered 4, extruded in grains 5 sized 100-2000 pirn 5 and dried 6 as represented in Figure 2.
• a bivalent tin oxy-hydroxide of the type SnxOy(OH)z with 1 ⁇ x ⁇ 6, 0 ⁇ y ⁇ 4 and 0 ⁇ z ⁇ 4, may be formed in the pH range 2-12.
• its synthesis in acidic environment with the presence of excess of H + ensures the high positive charge density in its surface, therefore, favoring the approaching of chromate anions (Cr0 4 2_ ) and providing higher uptake of chromium.
• it consists of 89 mg/L Na + , 40 mg/L Ca 2+ , 12.7 mg/L Mg 2+ , 183 mg/L HCOr, 50 mg/L S0 4 2 -, 71 mg/L CI " , 2 mg/L N-NO3-, 1 mg/L P , 0,04 mg/L P-PO4 3 - and 20 mg/L S1O2.
• Sn60 4 (OH) 4 is able to achieve residual concentrations lower than 1 pg/L, while its efficiency slightly increases when the pH increases in the range 7-8, which is the value for most drinking water containing Cr(VI).
• the adsorption capacity of Sn604(OH) 4 synthesized at pH 9 for residual Cr(VI) concentration 10 pg/L and adsorption pH 7.2 ⁇ 0.1 is estimated at 4.8 mg Cr(VI)/g, while for adsorption pH 7.7 ⁇ 0.1 the corresponding value reaches 6 mg Cr(VI)/g.
• the reaction pH is adjusted to 2 ⁇ 0.1 by the addition of a 30 % w/w NaOH solution.
• the pH is similarly adjusted to the 1 m 3 CSTR (2).
• the product flowing out from the CSTR (2) is directed to the thickening tank to remain under mild stirring for 24 h, then mechanically dewatered by either a centrifuge or by a filter-press, extruded in grains sized 100-2000 ⁇ and dried at 80-100°C.
• the produced material consists of a bivalent tin oxy-hydroxide with the structure Sn60 4 (OH)4 as represented in Figure 3.
• the reaction pH is adjusted to 4 ⁇ 0.1 by the addition of a 30 % w/w NaOH solution.
• the pH is similarly adjusted to the 1 m 3 CSTR (2).
• the product flowing out from the reactor (2) is directed to the thickening tank to remain under mild stirring for 24 h, then mechanically dewatered by either a centrifuge or a filter-press, extruded in grains sized 100-2000 ⁇ and dried at 40 °C.
• the produced material mainly consists of a bivalent tin oxide with the structure SnO referred to in Figure 4.
• the reaction pH is adjusted to 3 ⁇ 0.1 by the addition of a 30 % w/w NaOH solution.
• the pH is similarly adjusted to the 10 m 3 CSTR (2).
• the product flowing out from the reactor 2 is directed to the thickening tank to remain under mild stirring for 24 h, then mechanically dewatered by either a centrifuge or a filter-press, extruded in grains sized 100-2000 pm and dried at 80-100 °C.
• the produced material consists of a bivalent tin oxy-hydroxide with the structure Sn60 4 (OH)4.
• the reaction pH is adjusted to 10 ⁇ 0.1 by the addition of a 30 % w/w NaOH solution.
• the pH is similarly adjusted to the 10 m 3 CSTR (2).
• the product flowing out from the reactor 2 is directed to the thickening tank to remain under mild stirring for 24 h, then mechanically dewatered by either a centrifuge or a filter-press, extruded in grains sized 100-2000 ⁇ and dried at 40-100 °C.
• the produced material consists of a bivalent tin oxy-hydroxide (Sn60 4 (OH)4), as the major structural phase, with a small percentage of bivalent tin oxide (SnO) referred to in Figure 5.
• the synthesis method for bivalent tin oxy-hydroxide allows its production in granular units, so as to assist its use as a filling material in adsorption column beds, which is the only way of adsorbents application in large-scale.
• the production in a continuous flow reactor allows the accurate control of synthesis parameters, and as a result the optimization of adsorbents efficiency, while mild synthesis conditions favor high production rate at low cost implying to a minimum water treatment cost.
• accurate reaction control inhibits the production and release of toxic wastes to the environment.
• the adsorbent can be used for the removal of Cr(VI) from water supplied for drinking purposes since it is completely harmless for public health and does not involve byproducts formation which could potentially cause a reduction to the water quality. Its use is addressed to drinking water treatment units for house, municipal and industrial demands.
• table 1 provides a synopsis showing the differences between the method according to the invention and the cited documents which indicates the appearance of a number of distinguishing characteristics of the current invention. Table 1 below highlights these differences between the present invention and said reference documents.
• Current EP2 578 535
• the method of the invention refers to the synthesis of a remarkable adsorbent for hexavalent chromium, consisting of a positively-charged bivalent tin oxy-hydroxide with a structure Sn604(OH) 4 , under conditions which introduce a number of distinctive characteristics compared to other similar materials disclosed in the current state of the art.
• synthesis in continuous-flow operation and environmental temperature implies the possibility for illimitable quantities with low production cost.
• an extremely low fixed and operational cost is ensured when compared to other adsorbents of current state of the art.

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• Chemical Kinetics & Catalysis (AREA)
• Analytical Chemistry (AREA)
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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Environmental & Geological Engineering (AREA)
• Water Supply & Treatment (AREA)
• Solid-Sorbent Or Filter-Aiding Compositions (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)
• Water Treatment By Sorption (AREA)

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Citations (5)

• 2015
  • 2015-12-21 GR GR20150100548A patent/GR1008962B/el active IP Right Grant
• 2016
  • 2016-12-21 EP EP16834237.6A patent/EP3393652A1/en not_active Withdrawn
  • 2016-12-21 WO PCT/GR2016/000070 patent/WO2017109521A1/en active Application Filing

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