AU2018292424A1 - Stabilization of hazardous materials - Google Patents

Stabilization of hazardous materials Download PDF

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AU2018292424A1
AU2018292424A1 AU2018292424A AU2018292424A AU2018292424A1 AU 2018292424 A1 AU2018292424 A1 AU 2018292424A1 AU 2018292424 A AU2018292424 A AU 2018292424A AU 2018292424 A AU2018292424 A AU 2018292424A AU 2018292424 A1 AU2018292424 A1 AU 2018292424A1
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aluminum
arsenic
scorodite
gel
carbonate base
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AU2018292424B2 (en
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George DEMOPOULOS
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Royal Institution for the Advancement of Learning
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Royal Institution for the Advancement of Learning
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
    • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
    • B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
    • B09B3/20—Agglomeration, binding or encapsulation of solid waste
    • B09B3/25—Agglomeration, binding or encapsulation of solid waste using mineral binders or matrix
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
    • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
    • B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
    • B09B3/20—Agglomeration, binding or encapsulation of solid waste
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
    • B09C—RECLAMATION OF CONTAMINATED SOIL
    • B09C1/00—Reclamation of contaminated soil
    • B09C1/08—Reclamation of contaminated soil chemically

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  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Processing Of Solid Wastes (AREA)
  • Removal Of Specific Substances (AREA)
  • Solid-Sorbent Or Filter-Aiding Compositions (AREA)
  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)

Abstract

This invention relates to stabilization and/or solidification of hazardous materials which might be generated by activities like mining, milling or smelting industrial operations, such as arsenical wastes (such as scorodite, arsenic sulfides, calcium arsenates or arsenites, mixed calcium arsenates-phosphates, ferrous arsenate, ferric arsenite, or arsenic trioxide), antimony, mercury or selenium-containing wastes through the encapsulation of said arsenical wastes in the mineralized products of hydrolyzed aluminum gels created through the partial neutralization of A1(SO

Description

STABILIZATION OF HAZARDOUS MATERIALS
FIELD OF THE DISCLOSURE [001] This invention relates to stabilization / solidification of hazardous materials and, in particular, arsenical wastes through encapsulation with mineralized products of hydrolyzed aluminum gels.
BACKGROUND OF THE DISCLOSURE [002] Hazardous materials generated by different industries call for treatment and containment in waste management facilities to ensure that there is no release to the environment of toxic elements. Arsenic is a major environmental hazard in many mining, milling or smelting operations that requires proper immobilization and disposal. Among the preferred treatment approaches to the arsenic problem in the minerals/metals industry is to co-precipitate it to ironarsenate solids by neutralization with lime. While this route may be suitable for dilute sources of arsenic, it is not amenable to arsenic-rich sources. In the latter case, the immobilization of arsenic - released during pyrometallurgical or hydrometallurgical processing of arsenic-containing ores in the form of scorodite (FeAsO^ -2H2O) is advocated due to its high arsenic content (-23%) and relatively low solubility. A special issue related to the stability of scorodite, however, is its decomposition under alkaline (pH>7) and anaerobic/anoxic conditions that may develop over time if not properly disposed.
[003] Stabilization/solidification (S/S) is an approach used for the fixation of toxic waste materials of various types and sources. An example of such a process involves the mixing of a toxic waste with cement and/or other binder materials to produce a chemically and physically stable solid mass suitable for use in the landfill. Amongst the most common technologies currently used for the stabilization/solidification of hazardous wastes are those based upon
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PCT/CA2018/050790 hydraulic cement and/or slaked lime and, less commonly, organic polymers, sulphur polymer cement, and other encapsulation materials.
[004] Stabilization/solidification of arsenic-containing compounds using Portland cement could reduce the mobility of arsenic by formation of insoluble hydroxides, carbonates, or silicate providing sorption; or simply physical encapsulation. However, cement-based stabilization/solidification is not a robust long-term option for iron arsenate type solids like scorodite because the process creates a highly alkaline environment (pH -12.5) that would lead to the release of arsenic.
SUMMARY OF THE DISCLOSURE [005] In one aspect, there is provided a method for the stabilization of hazardous materials comprising:
a) forming a hydrolyzed aluminum gel by partial neutralizing, in an aqueous medium, Al(SO4)i.5 with a carbonate base;
b) blending said hydrolyzed aluminum gel and hazardous material; and
c) storing said blend from the preceding step to obtain a mineralized aluminum (oxy) hydroxide/hazardous material composite.
[006] In a further aspect, there is provided the use of carbonate base (such as NaHCCh or Na2COs) -derived hydrolyzed aluminum gels and their mineralized products in stabilization of hazardous materials.
[007] In a further aspect, there is provided a composite comprising scorodite particles and a gel-derived solidified matrix comprising aluminum (oxy)hydroxide mineral phases.
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PCT/CA2018/050790 [008] In a further aspect, there is provided a composite prepared by the method as defined herein.
BRIEF DESCRIPTION OF THE DRAWINGS [009] Embodiments of the present disclosure will now be illustrated with reference to the attached Figures, wherein:
FIG. 1 is a graph of the evolution profiles of pH and Eh with time during stability testing of scorodite-gel blends using either Na2SO3 (top) or Na2S (bottom) to adjust Eh;
FIG. 2 depicts arsenic release from naked scorodite and scorodite encapsulated with aluminum gels derived from reference bases NaOH and Mg(OH)., compared to a carbonate base (Na2CO3 ) of this disclosure, under oxic condition;
FIG. 3 depicts arsenic release from naked scorodite and scorodite encapsulated with aluminum gels derived from reference bases NaOH and Mg(OH)2, compared to a carbonate base (Na2CO3 ) of this disclosure under anoxic condition;
FIG. 4 is a graph showing the arsenic release from naked scorodite and scorodite encapsulated with Al-gels prepared from NaOH, Na2CO3 and NaHCOs under anoxic (Na2SO3) condition and pH~9;
FIG. 5. represents the arsenic release from scorodite encapsulated with aluminum gels derived from Na2CO3 and NaHCO3 under anoxic condition chemically generated with Na2S',
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FIG. 6 depicts XRD patterns of Naf'O-. derived aluminum gels after 167 days stability testing under oxic and anoxic conditions;
FIG. 7 presents the profile of arsenic release from scorodite encapsulated with Al-gels prepared from Na2CC>3 or Mg(OH)2 under oxic (with and without elemental sulfur present) or anoxic (Na2S) condition (with or without elemental sulfur present) in water of pH~9 compared to release of arsenic under same conditions from naked scorodite; and
FIG. 8 is a schematic representation of scorodite particle encapsulated with gel-derived mineralized aluminum (oxy)hydroxides phases.
DETAILED DESCRIPTION OF THE DISCLOSURE [0010] The inventors have discovered hydrolyzed aluminum gels derived from aluminum sulfate solutions by neutralization with carbonate bases to be highly effective in encapsulating hazardous materials like scorodite particles. The said aluminum gels form a mineralized matrix protecting the scorodite particles from decomposition in alkaline or anoxic waters, hence minimizing release of arsenic.
[0011] The encapsulation process involves blending scorodite particles with gels prepared with carbonate bases from aluminum sulphate solution and storing the resultant composite that provides protection via the in situ formation of a mineralized aluminum (oxy)hydroxide matrix.
[0012] The stability of encapsulated scorodite was examined in the laboratory by performing leachability tests under alkaline (pH 8-9) oxic or chemical reducing (anoxic) conditions, demonstrating effectiveness in curtailing arsenic release.
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PCT/CA2018/050790 [0013] In one embodiment, the carbonate base is comprising a carbonate anion (formula: CO32 ) or bicarbonate anion (formula: HCO3' - also referred to as hydrogen-carbonate ion in the IUPAC system).
[0014] Suitable carbonates include:
carbonates L12CO3, Na2CO3, K2CO3, etc.
Alkali metals bicarbonates L1HCO3, NaHCCf. KHCO3, etc.
carbonates MgCCf. etc.
Alkaline earth metals bicarbonates Mg(HCC>3)2, etc.
carbonates ZnCC>3, FeCCh, etc.
Other metals bicarbonates Zn(HCC>3)2, Fe(HCC>3)2, etc.
[0015] In one embodiment, the carbonate base is NaHCCh or Na2CO3.
[0016] In one embodiment, the molar ratio of Al: As (Al from AI (SO ., )j 5 and As from scorodite) is ranging from about 1.5 to 0.05; preferably less than about 1, or from about 1.0 to 0.1, or less than about 0.2, or more preferably from about 0.2 to 0.1, and most preferably about 0.1.
[0017] In one embodiment, the concentration of Al(SOftXi in the aqueous medium for preparing the Al gel is ranging from about 0.5 to 3.0M (mol/L) of 1.0 to 3.0 mol/L; preferably, about 1.0 to 2.0, more preferably about 1.5 to 2.0, and most preferably about 2.0.
[0018] The carbonate bases can be used as powders or suspension/solution. In the case of Na2CC>3, from about 0.5M to dry powder and preferably about 1.0M to 6M, more preferably about 2M to 4M and most preferably about 2.5 to 3M. In the case of NaHCCh, one can double
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PCT/CA2018/050790 these numbers, i.e. from about IM to powder, or about 2M to 12M or about 4M to 8M or most preferably about 5 to 6M. The amount will suitably vary depending on the concentration of Al sulfate solution. The skilled person understands that it may not be desirable to use very dilute solutions of base or AI-SO4 as this would lead to very liquid-like gel. On the other hand, it may not be desirable to use too concentrated a medium as this leads to immediate solidification (in the form of crushed ice) of the gel, and making more difficult its handling, such as its transportation to the storage site.
[0019] In one embodiment, the molar ratios of carbonate bases to Al is between about 2<0.5CO32'=HCC>37Al < about 3 or preferentially between about 2.2 and 2.8 or more preferentially about 2.4 to 2.6 and most preferably about 2.5.
[0020] In one embodiment, the temperature range for forming the gel or blending it with the hazardous material is from about 0 to 80°C, or preferably about 10 to 40°C, or more preferably about 15 to 30°C or about 20°C.
[0021] As used herein, “hazardous materials” subjected to stabilization with hydrolyzed aluminum gels as defined herein is not especially limited. Examples include ferric arsenate/scorodite, but however may as well be other arsenical compounds, residues, precipitates or flue dusts such as arsenic sulfides, calcium arsenates or arsenites, mixed calcium arsenatesphosphates, ferrous arsenate, ferric arsenite, arsenic trioxide and so on. Further, the carbonatederived aluminum gels could be used to provide additional protection to arsenical residues previously stabilized (partially) with conventional cement based methods. Finally, the gels could be used for other types of hazardous materials, as is the case for example of antimony, mercury or selenium-containing wastes generated by smelting and other industrial operations.
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PCT/CA2018/050790 [0022] As used herein, “blending” may involve aging following mixing of the gel and the hazardous arsenical material or not before permanent disposal. Non-limiting examples of aging time may be about one day or from 1 day to 30 days before permanent disposal (storing) of the blended material.
[0023] As used herein, “aqueous medium” can be essentially water, optionally comprising conventional additional components present in the “hazardous materials” subjected to stabilization with hydrolyzed aluminum gels as defined herein.
Experimental
Preparation of Scorodite [0024] The scorodite substrate material was synthesized by atmospheric precipitation via the use of a seed and supersaturation control method previously developed by the inventors. In this procedure, 0.5 L As(V)-Fe(IH)-H2SO4 solutions containing 40 g/L arsenic(V) and iron(III) to arsenic molar ratio of one were placed in a reactor and heated to 95°C. When the temperature inside the reactor reached ~65°C and the pH had dropped to 0.45, 5 g of hydrothermally produced scorodite were added to the reactor as seed. In the presence of seed, precipitation started and was allowed to proceed for 24 hours, after which the slurry was filtered using a pressure filter with 0.22 pm pore size membrane filter. Solids were then subjected to several washing and consecutive TCLP-type washing steps (TCLP stands for Toxicity Characterization Leachability Procedure-method developed by the Environmental Protection Agency-EPA- of the USA). The freshly washed scorodite particles were subsequently used in aging with aluminum hydroxyl gels. All the reagents and chemicals used were of analytical grade.
Synthesis of Aluminum Gels [0025] Preferred gels were prepared using sodium bicarbonate (NaHCCfi) and sodium carbonate (Na2CO3) by partial neutralization of aluminum(III) sulfate solution. Aluminum gels derived
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PCT/CA2018/050790 from NaOH (as reference gel) were produced by partial (molar ratio OH:A1 = 2.5) quick neutralization of 2 mol/L AljSO,)j 5 solutions with 5.0 mol/L NaOH at room temperature. For producing the other two types of gels, magnesium hydroxide (also as reference gel), sodium carbonate and sodium bicarbonate, powders or previously dissolved or suspended in water (as reported in the specific examples given) were introduced to the prepared AI(SOa\5 (typical concentration: 2 mol/L) solutions. Mild stirring had to be applied during mixing as excessive force was found to be counter-productive, causing gel thinning. The freshly prepared aluminum gels were used to stabilize scorodite particles.
Blending of Scorodite with Aluminum Gels [0026] The scorodite and aluminum-based gels were blended together and subsequently allowed to age at room temperature for 7 days. A low gel/scorodite ratio (Al : As = 0.1 molar basis) was applied for blending the two products. The procedure involved aging the blends in sealed Erlenmeyer flasks before initiating stability testing.
Stability Testing [0027] The scorodite-gel blends were subjected to stability testing - alongside naked scorodite as control - in pH 8-9 water under oxic and anoxic (using Na2S or Na2SO2 chemicals as reducing agents) conditions. In addition to the carbonate-based gels disclosed herein, reference examples were prepared from NaOH and Mg(0H)2 neutralized gels. Solids were placed in sealed 250 mL Erlenmeyer flasks with 100 mL of de-ionized water and agitated with an orbital shaker over extended periods of time while regularly adjusting pH and oxidation-reduction (EQ potential to monitor the release of arsenic via sampling and ICP analysis. The liquid to solid ratio (L/S) was kept at 20 for all tests. Typical pH and Eh evolution data during stability testing are shown in FIG 1.
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Oxic Stability Test [0028] The stability of various materials was studied as a function of time under oxidizing conditions at room temperature. The stability was evaluated by equilibrating these solids in deionized water that was initially adjusted to pH = 9 ± 0.2 with 0.5 mol/L Ca(OHf slurry. The system pH was allowed to drift down to pH = ~7.5 and subsequently readjusted. Refer to FIG. 1.
Anoxic Stability Test (Na/SOft [0029] This anoxic stability test was conducted at adjusted reducing potential (Eh) conditions (200 ± 20 mV ) via the addition of sodium sulfite (0.15mol/L NajSOft solution. The pH of the solution was monitored and periodically adjusted to pH 9 ± 0.2 with 0.5 mol/L Ca(OH)2 slurry. Refer to FIG. 1.
Anoxic Stability Test (Na?S) [0030] This anoxic stability test was conducted at adjusted reducing potential (Eh) of 50mV via addition of sodium sulfide solution (0.125M Na2S). The pH of the solution was monitored and periodically adjusted to pH 9 ± 0.2 with 0.5 mol/L Ca(OH)2 slurry. Refer to FIG. 1.
[0031] For both oxic and anoxic tests, samples were taken on a regular basis with 10 mL plastic syringes, which were filtered with a 28 mm diameter syringe filter with 0.2 pm pore size and diluted with acidified (HNO 3) de-ionized water in preparation for chemical analysis. The measurement of the pH was achieved with a refillable double-junction electrode with an accuracy of ± 0.1 pH units. The Eh was measured using a platinum single-junction combination electrode (Ag/ AgCl) with a reported accuracy of ± 20 mV. All experiments were performed at room temperature (22 °C).
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Analysis and Characterization [0032] The concentrations of arsenic in aqueous samples were analyzed using an Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP-AES). Chemical analysis of solids was performed by ICP-AES following their acidic digestion.
[0033] Powders were characterized by X-ray powder diffraction using a X-ray diffractometer (D8 Discover Bruker) with Cu K a radiation (λ= 1.5405 A).
Results and Discussion
Encapsulating material [0034] For the context of scorodite encapsulation/stabilization, an aluminum gel of acceptable quality for ageing tests is one that has a sufficiently high initial viscosity (at least 300 cP) to enable solid particles to be blended with the gel without subsequently settling. It is also preferable that the aluminum gel maintains a sufficiently high viscosity for enough time (e.g. 1 to 24 hours) for ease of transportation to storage site before it becomes solidified.
[0035] In the following examples, the preparation of Al-gel was conducted via the partial quick neutralization (molar ratio 0.5CC>32'=HCO37Al = 2.5) of Al/SOJis solution with the base at room temperature. The resulting mixture was mildly stirred until a gel-like consistency was achieved.
[0036] Tables 1-4 below summarizes some of the viscosity measurements. The measurements were made with a Brookfield LVDV-E Viscometer apparatus.
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PCT/CA2018/050790 [0037] Table 1 - NaOH pellets, Na2COs, NaHCCfi powders were introduced to a 2M AflSOfii.s solution.
Base Initial Viscosity (cP) pH
NaOH 366 4.55
Na2CO3, N/A N/A
NaHCO3 328-5000 N/A
[0038] Table 2 - Na2CC>3, NaHCCfi powders were introduced to a IM AftSOfli.s solution.
Base Initial Viscosity (cP) pH
Na2CO3, 171,600^ >200,000 5.07
NaHCO3 >200,000 5.01
[0039] Table 3 - Na2CO3, NaHCCfi powders were introduced to a 0.5M A1(SC>4)i.5 solution.
Base Initial Viscosity (cP) pH
Na2CO3, 252* (*liquid-like gel) 4.93
NaHCO3 344 5.50
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PCT/CA2018/050790 [0040] Table 4 - Solutions of 5.0M NaOH, 2.5M Na2CO3, and 5.0M NaHCOs suspension were introduced to a 2M Al/SOty.s solution.
Base Initial Viscosity (cP) pH Viscosity in 24 hours (cP)
NaOH 411 5.32 519* (*water/gel separation)
Na2CO3, 150 800—> >200,000 5.03 805
NaHCO3 >200,000 4.67 408
[0041] As shown in Tables 1 to 4, NaHCOs and Na2CO3 provided satisfactory initial viscosities under various reaction conditions except for very dilute (0.5M-Table 3) Al/SOty.s solution. In addition, tests showed gels made with NaOH suffered breakage with time, i.e. water/gel separation (Table 4).
[0042] For each aluminum gel (NaOH , Mg(OH)2, and Na2CO3 ), the corresponding X-ray diffraction pattern was generated. It was observed that all the gels after washing and drying exhibit an identical X-ray diffractogram revealing an amorphous nature. No crystalline compound containing aluminum could be confirmed.
Stability under Oxidizing Environment [0043] The arsenic release in terms of As concentration as a function of time for the scorodite encapsulated with aluminum gels made with three different bases, Na2CO3, NaOH, or Mg(0H)2 along with the atmospherically produced scorodite control material is shown in FIG. 2. It is observed that arsenic release was effectively reduced by the encapsulation with hydrolyzed aluminum gels. The release of arsenic from scorodite substrate was in the order of 8.8 mg/L at pH 7.1 after 167 days of stability testing. Specifically, scorodite encapsulated with the gel deriving from Na2CO3 exhibited a negligible amount of arsenic release after 167 days, and was below the detection limit of the ICP-AES for arsenic (i.e. <0.1 mg/L) at a final pH of ~7.6. This
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PCT/CA2018/050790 is significantly lower than the permitted amount of released arsenic in leachate from industrial/mining waste ranging from 1.0 mg/L in certain countries like Japan to 5.0 mg/L in USA. Therefore, these gels display a superior performance for industrial usage. It was also observed that the arsenic released from the two types of hydroxide ions (i.e. NaOH and Mg(OH)2) varied broadly and in an unexpected manner relative to each other.
Stability under Anoxic Environment [0044] FIG. 3 shows the arsenic release versus time for various aluminum gel/scorodite materials in comparison with scorodite substrate under anoxic environment (chemically generated under Na2SO3). It can be seen that the dissolution of scorodite (-137 mg/L in the case of naked mineral) was effectively suppressed with the aid of these aluminum gels encapsulations. The concentration of arsenic released from scorodite encapsulated with particular aluminum gels was reduced by at least one order of magnitude. The scorodite encapsulated with the sodium hydroxide -derived gels had a significantly higher arsenic release. For example, the NaOHderived gel released 4.2 mg/L (at pH = 8.3) compared to the sodium carbonate gel showing 2.7 mg/L (at pH = 8.7) after 167 days. The magnesium hydroxide gel sample had an arsenic release of 19.9 mg/L (at pH = 8.4). Therefore, once again, it was observed that the arsenic released from the two types of alkaline ions (OH' vs. CO32' or HCO3') varied broadly.
[0045] A similar trend (i.e. carbonate gels better than NaOH gel) was observed in another series summarized with the data in FIG. 4. It can be seen that the scorodite encapsulated with the gels generated with the two carbonate bases released less arsenic (0.2-0.5 mg/L As) than the sample with the gel made with NaOH (1.7 mg/L As) after 62 days of contact with water. By comparison, the release of arsenic from naked scorodite under the same anoxic (Na2SO3, pH -9) condition was 17 mg/L.
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PCT/CA2018/050790 [0046] FIG. 5 shows the arsenic released from scorodite encapsulated with aluminum gels derived from Na2CO3 and NaHCO3 under anoxic conditions (chemically generated with Na2S). During the 30-day stability test, the arsenic released from the scorodite encapsulated with Al-gel derived from NaHCO3 is no more than 0.1 mg/L and lower than that from Al-gel derived from Na2CO3.
[0047] Further evidence of the effectiveness of hydrolyzed aluminum gels generated with a carbonate base (this time Na2CO3) is provided with the data of FIG. 7. It can be seen that the encapsulation of scorodite with Al-gels improves its stability in both oxic and anoxic conditions. In this case, Na2S was used as reducing agent and the pH was -9. The current results show that scorodite encapsulated with the Na2CO3 Al-gel -prepared by addition of Na2CO3 powder into 2M A1(SO4)i.5 solution- has released less arsenic (-0.5 mg/L) than “naked” scorodite by a whole order of magnitude. Moreover, the stability of Al-Gels hydrolyzed using Na2CO3 performed better than Mg(OH)2 based gels. In some tests elemental sulfur -a common ingredient in some industrial arsenical residues- was added to assess possible adverse effect on stability without such evidence.
Post Stability Testing Characterization [0048] XRD analysis of the Na2CO3 -derived aluminum gels before and after stability testing demonstrated a transformation of the amorphous aluminum gel into mineralized crystalline A100H or A1(OH)3 phases (FIG. 6). Patterns of the Na2CO3 -derived aluminum gels exhibit an amorphous nature with broad peaks appearing at approximately2Θ = 20°,40°,60°. After 167 days stability testing under oxic conditions, sharp lines developed that were entirely due to the amorphous-to-crystalline phase transformation. The amorphous aluminum gel was converted into a mineralized matrix made of gibbsite and bayerite ΑΐΙΟΗ), crystalline phases.
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PCT/CA2018/050790 [0049] In the meantime the aluminum gels after 167 days stability testing under chemically generated anoxic condition had also converted into mineralized phases; this time matching the boehmite (A1OOH) crystalline phase.
[0050] The in-situ mineralization of the hydrolyzed aluminum gel into inert aluminum (oxy)hydroxide crystalline phases as schematically depicted in FIG. 8 provides a protective layer to the scorodite particles, thus preventing their dissolution/decomposition. The mineralized aluminum (oxy)hydroxide matrix is immune to pH and redox potential swings compared to those caused by the addition of chemical reducing agents, hence greatly enhancing the stabilization of the toxic material.

Claims (17)

  1. What is claimed is:
    1. A method for the stabilization of hazardous materials comprising:
    a) forming a hydrolyzed aluminum gel by partial neutralizing, in an aqueous medium, AhSOfli.s with a carbonate base;
    b) blending said hydrolyzed aluminum gel and hazardous material; and
    c) storing said blend from the preceding step to obtain a mineralized aluminum (oxy) hydroxide/hazardous material composite.
  2. 2. The method according to claim 1, wherein said step of forming said hydrolyzed aluminum gel is comprising adding said carbonate base to an aqueous medium comprising said A1(SC>4)i.5.
  3. 3. The method according to claim 1 or 2, wherein the concentration of ri/(SO4)15 in the aqueous medium is from about 1.0 to 3.0 mol/L.
  4. 4. The method according to any one of claims 1 to 3, wherein said carbonate base is NaHCCL or Na2CO3.
  5. 5. The method according to any one of claims 1 to 4, wherein said carbonate base is Na2CO3 powder or NaHCO3 powder.
  6. 6. The method according to any one of claims 1 to 4, wherein said carbonate base is a suspension/solution of Na2CO3 at a concentration of about 2M to 4M or of NaHCO3 at a concentration of about 4M to 8M.
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    PCT/CA2018/050790
  7. 7. The method according to any one of claims 1 to 6, wherein said carbonate base is present at a molar ratio of carbonate base to Al of between about 2<0.5CO32'=HCC>37Al < about 3.
  8. 8. The method according to any one of claims 1 to 7, wherein said hazardous material is comprising arsenic (As), and in said step of blending said hydrolyzed aluminum gel and said hazardous material, the aluminum to arsenic molar ratio is lower than about 1.
  9. 9. The method according to claim 8, wherein said hazardous material is arsenical waste generated by mining, milling or smelting industrial operations.
  10. 10. The method according to any one of claims 1 to 9, wherein said hazardous material is ferric arsenate known as scorodite (FeAsO4.2H2O).
  11. 11. The method according to any one of claims 1 to 8, wherein said hazardous material is arsenic sulfides, calcium arsenates or arsenites, mixed calcium arsenates-phosphates, ferrous arsenate, ferric arsenite, or arsenic trioxide.
  12. 12. The method according to any one of claims 1 to 7, wherein said hazardous material is an antimony, mercury or selenium-containing waste.
  13. 13. The method according to any one of claims 1 to 12, wherein after said blending, the resulting blend is aged for one to seven days before said step of storing.
  14. 14. The use of carbonate base (NaHCCfi or Na2CO3) derived hydrolyzed aluminum gels and their mineralized products in stabilization of hazardous materials.
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    PCT/CA2018/050790
  15. 15. A composite comprising scorodite particles and a gel-derived solidified matrix comprising aluminum (oxy)hydroxide mineral phases.
  16. 16. The composite of claim 15, wherein said phase is comprising crystalline and poorly crystalline A100H (boehmite and pseudoboehmite) or the polymorphs of A1(OH)3 gibbsite, bayerite and nordstrandite.
  17. 17. The composite of claim 16, wherein said A100H or A1(OH)3 mineral phases are obtainable from hydrolyzed aluminum sulfate gels produced by partial neutralization with a carbonate base.
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