AQUATECH Co.,Ltd.

Technology to detoxify cyanogen

 Though cyanogen/cyanide is deadly poisonous,it is widely used because of its superior chemical characteristics. So it may happen to generate in produce manufacturing even without using cyanogen compound in the process.
 A.Ohnish, founder of Aquatech has devoted years of  his life,to study on detoxification of cyanogen/cyanide and developmen of treatment technology for that. It is required to vary the way to treat cyanogen/cyanide according to its existence form, wastewater load, concentration and coexisiting materials.
 We are ready to offer a suitable treament process for cyanogen/cyanide
based on wealth of knowledge, experience, technical strength and know-how.

Solution for treatment of cyanogen/cyanide in waste water

There are the following methods to treat cyanogen/cyanide in waste water.

  1. Oxidation decomposition method (Alkaline chlorination,Ozone oxidation,Electrolytic oxidation)
    Most of cyanogen/cyanide containing wastewater is treated by alkaline chlorination method.Cyanogen is transformed to cyanic acid by mixing with sodium chlorite gradually at pH of 10 or higher checking ORP value. (1st step) Then formed cyanic acid is decomposed to nitrogen and carbon dioxide. Thus cyanogen/cyanide is detoxiffied.This method is suitable for wastewater containing several hundred mg/L of cyanogen/cyanide ion. It can decompose also metal-cyanogen complexes except those of iron ,cobalt,gold,nickel and silver. Iron-cyanogen complex is hardly decomposed by this method. Facilities for alkaline chlorination
    "

             Facilities for alkaline chlorintion

  2. Insoluble complex method (Prussian blue method, Zinc white method, Reduced copper method)
    Iron-cyanogen complexes([Fe(CN) 6] 4-)are hardly decomposed by alkarine chlorination described above.
    These complexes form poorly-soluble compounds(Fe4[Fe(CN)6]3, Fe3[Fe(CN) 6]2, Fe2[Fe(CN) 6]),when mixed with excess iron ions.Those compounds precipitate from wastewater and can be removed with solid-liquid separator such as filter press. Though Prussian blue method generates cyanogen containing sluge,it is an effective way to remove iron-cyanogen complex from wastewater and it is advantageous that ferrous sulfate commomonly used fot this treatment is inexpensive. So by using the nature that Fe2[Fe(CN)6] is a poorly-solublecompound cyanogen/cyanide is precipitated as insoluble compound by feeding ferrous ion Recently Prussian blue attracts attention as fixing agent for radioactive cesium.We made an announcement of an adsorption treatment system for cesium containing wastewater on April 26,2011 shortly after the nuclear accident. Zinc white method is used only for wastewater of low concentration of cyanogen/cyanide from the following reassons. 1.Zinc chloride used is expensive.
    2.Excess zinc forms complex with ammonia in wastewater, being formed by partial hydrolysis of cyanogen. It is difficult to reduce zinc to regulatory level, 2mg/L or lower> by treating the zinc-ammonia complex with conventional hydrooxide method.

    Facilities for prussian blue method and Filtering dehydrator
                   Prussian Blue Method

  3. Hydrothermal treatment(Thermal hydrolysis method.Wet oxidation method)
    Thermal hydrolysis method is suitable for treatment of wastwater containning high concentration of cyanogen/cyanide(2,000 〜50,000 mg/L).When cyanogen/cyanide containing wastewater is kept at high temperaturs(170〜260℃)in autoclave, hydrolisis occurs as Equation (1) or (2),and cyanogen decomposes to ammonia and formic acid. NaCN + 2H2O = HCOONa + NH3    (1)
    Na4Fe(CN)6 + 2NaOH + 11・H2O + 1/6・O2 = 6NH3 + 6HCOONa +1/3・Fe3O4    (2)
    Most coexxisiting metal species precipitate as elemental substances(Au,Pt,etc.) or oxides (Fe3O4 etc.). Some metas form ammonia complexes and dissolve in water. Advantages of this method
    @No chemicals are required to decompose cyanogen/cyanide since hydrolys is reaction with water
    AVolume of formed sludge is small.
    BWhen precious metals are contained in the wastewater, they can be recovered as elemental substances. CThis method is unexpectedly energy-saving and the running cost is small because little latent heat of vaporization is required and heat recovery is possible since the reaction is carried out inside pressure vessel.
    DPossible to decompose easily iron-cyanogen complex which is difficult to treat by alkaline chloridnation.
    EPossible to treat efficiently wastewater containing cyanogen/cyanide of high concentration.
    Disadvantages
    @Necessary to treat ammonia and formate of organic pollution generated.
    ACost of equipment is high.

    Facilities for thermal hydrolysis    Scruber for HCN gas
          Facilities for thermal hydrolysis                Scrubber for HCNgas

  4. Microorganism treatment
    Suitable for wastewater containing cyanogen/cyanide of low concentration.
  5. Others
    Please consult us when you have problems with the following. 1)Treatment method for hydrocyanic acid gas,cyanogen/cyanide containning sluge or polluted soil/groundwater.
    2)Analytical technologies for cyanogen in waste materials.

  1. Technology for gold recovery with cyanogen/cyanide

  2. Gold smelting at gold mines has been practiced using cyanide widely for years.
    Moreover,gold plating is widely carried out in electronic industry and wastewater containing high concentration of gold cyanide is discharged.
    Further it is actively practced to recover gold from urban mine such as gold-plated electronic parts by dissolving with cyanide.
    Among various treatment technolgies for cyanogen/cyanide, thermal hydrolysis is the most excellent method for detoxification of cyanogen/cyanide and recovery of gold,silver and so on.
    Below is given explanation how our proprietary technology works to recover precious metals.
    In recovery of gold from milled gold ore(Fig 1-1) or gold-plated parts(Fig 2) using sodium cyanide, gold is eluted with cyanide according to Equation(1). Silver is similarly
    eluted with cyanide according to Equation(2).
    4Au + 8NaCN + 2H2O + O2 = 4Na[Au(CN)2] + 4NaOH     (1)
    4Ag + 8NaCN + 2H2O + O2 = 4Na[Ag(CN)2] + 4NaOH     (2)

    Gold ore before cyanide elution          Residue after cyanide elution

    Fig1-1 Gold ore before cyanide elution         Fig1-2 Residue after elution

    Gold-plated parts

    Fig2 Gold-plated parts


    2Na[Au(CN)2] + 2NaOH + 7H2O = 2Au↓+ 4NH3 + 3HCOONa + NaHCO3
    2Na[Ag(CN)2] + 2NaOH + 7H2O = 2Ag↓+ 4NH3 + 3HCOONa + NaHCO3

    Cyanogen reacts with water to form ammonia and formic acid(salt),and gold or silver
    separates out as powder of metal element(Au0,AgO) compactly. As shown in Fig3 base
    metals and precious metals separate out at different temperature in thermal hydrolysis.
    Thus precious metals and other metals can be recovered separatetly by conducting thermal hydrolysis at defferent temperatures.
    Utilizing these characteristics, treatment flow can be set up as outlined in Fig 4.

    Hydrolisys Temperature of Metal-Cyanogen Complex

           Fig3 Hydrolysis Temperrature of Metal-Cyanogen Complex


    Thermalhydrolyi flow for reovery of precious metalsx

              

    Fig4 Flow Sheet of Thermal Hydrolysis System


    Practical examples of thermal hydrolysis given below exemplify uniquely high
    decompositin rate of cyanogen and recovery rate of gold/silver achieved by the method.

    Table 1 shows analytical values before and after thermal hydrolysis treatment
    conducted on 7 lots of cyanogen wastewater containing gold and other maetals at a
    company for precious metal recovery. Gold,silver and other precious metals are
    recovered rates of almost 100% and 99.94% of cyanogen is decomposed.

             Table 1
    Thermal  hydrolysis results of 7 lots waste
    Table2 shows analytical values(average) before and after of thermal hydrolysis conducted on 12 batches of cyanogen wastewater at joint treatment center for plating
    waste solution.Cyanogen contaimed in high concentration is decomposed at arate of 100%.As shown in Table3,from analyticl values(average) of sludges generated in thermal hydrolysis of other 4 batches of waste water,it turned out that gold of 475g and silver1 of 12.5Kg on average are containded in 1 ton of the sludge and hence the sludge obtaind is of high-value.

               Table 2
    Practical example2 Thermal hydrolysis results of 12 batches
    Table3 Practical example3 Thermal hy drolysis results of 12 batches (Joint treatment center for palting wast solution) [unit(contents of CN,metals):mg/L] (Joint treatment c
    enter for palting wast solution)

                Table 3
    Practical example3 Thermal hydrolysis results of 4 batches

Recovery of precious metals from printed boared of Japanese pinball machine


   As shown in Table4,printed board(Fig.5) of used Japanese pinball machine contains
   plenty of precious metals and has high-value.Those precious metals can be recovered
   with high efficiency by cyanogen dissolution and the following thermal hydrolysis and
   large benefit is expected to be obtained.

          Fig 5 Printed boards of used Japanese pinball machine

Printed board of used Japanese pinball machine
            

           Table 4 Value of metals in printed boards of 200,000 units of pinball machine. Value of metals in printed boards of 200,000 units of pinball machine Printed boaerd of used Japanese pinball



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