Precipitation of arsenic by ferrous or ferric ion is relatively simple and better option for effluents having high concentrations of arsenic. The precipitated arsenic bearing product is also stable in the normal environmental conditions. The stability accounts for the immobility of arsenic to the environment.
Full Answer
How to remove arsenic from gold processing waste water?
A process based on the precipitation of barium arsenate appears to be applicable to the treatment of arsenic from gold processing waste water. The high cost of reagents may be an important consideration.
Which method is used for arsenic removal from drinking water?
The precipitation/coprecipitation method was used for arsenic removal from drinking water by ferric chloride, ferric sulfate and ferrous sulfate as coagulant.
How do you classify arsenic compounds?
Arsenic compounds can be classified into three major groups: arsine gas. As (III) (trivalent, 3 oxidation state, such as arsenites), As (V) (pentavalent, 5 oxidation state, such as arsenates), and Arsine Gas (-3 oxidation state). The relative toxicity of an arsenical depends primarily on rates of absorption and elimination [ATSDR 2007].
How to treat arsenic (111)?
The choice of a treatment method depends also on the oxidation state of arsenic in solution. Arsenic (111) can only be oxidised to arsenic (V) under fairly severe conditions such as those obtained using ozone or with high temperature – high pressure oxygen, so that the barium arsenate process, for example, would need an oxidation stage.
How do you precipitate arsenic?
Arsenic is precipitated as As2S3 with either H2S or NaHS in a number of these processes. The processes are not related to gold processing but are applicable in that area. Arsenic in groundwater is largely the result of minerals dissolving from weathered rocks and soils.
What is arsenite arsenate?
Arsenic exists in two oxidation states—arsenate, As(III), and arsenite, As(V)—both of which are anions (see also Chapter 8). Although both forms are toxic, arsenite is much more toxic and is also very soluble and mobile in water environments.
How do you remove arsenic from wastewater?
A cost-effective approach for arsenic removal is coagulation and precipitation (chemical processes) followed by filtration (a physical process), which is termed coagulation/filtration (CF) in the water treatment industry. Common coagulants used for arsenic are iron salts and aluminum sulfate (alum).
How does iron remove arsenic from water?
Arsenic can be removed via two primary mechanisms: adsorption and coprecipitation. First, soluble iron [Fe(II)] and As(III) are oxidized. The As(V) then adsorbs onto the iron hydroxide precipitates that are ultimately filtered out of solution.
What is the Valency of arsenate?
5Arsenates are salts or esters of arsenic acid. The arsenic atom in arsenate has a valency of 5 and is also known as pentavalent arsenic or As(V). Arsenate resembles phosphate in many respects, since arsenic and phosphorus occur in the same group (column) of the periodic table.
How is arsenate formed?
Typically, they form at the expense of primary arsenic or vanadium-rich minerals by weathering and oxidation processes; some may have been precipitated in reducing hydrogen sulfide-rich environments.
What pH does arsenic precipitate?
Arsenic(V) can also be precipitated from process solutions below about pH=2 with iron(III) to form ferric arsenate, FeAsO4. 2H2O, which is white to very pale green in color.
How is arsenic waste treated?
Under the condition of strong acid, 99.9% arsenic can be removed by direct injection of hydrogen sulfide[8] into the waste liquid. The reaction product is arsenic sulfide. Peidong Wang[9] used arsenic removal in two steps to treat arsenic waste water.
What type of filter removes arsenic from water?
Reverse Osmosis (RO)The best water filtration system to remove arsenic from your drinking water is none other than a Reverse Osmosis (RO) water filtration system. Reverse Osmosis, also known as RO, is a process that uses pressure to force water through a special semi-permeable membrane to remove dissolved pollutants.
How does water precipitate iron?
One highly useful technique in the treatment of water with an alkali such as soda ash to raise the pH of the acid water and chlorine to precipitate the iron. With such treatment, a simple carbon filter can be used to remove the insoluble iron from the water.
What is the difference between arsenic 3 and 5?
In groundwater, arsenic usually occurs in two forms: trivalent arsenic (As+3, or arsenite) or pentavalent arsenic (As+5, or arsenate). Both are harmful to humans, but trivalent arsenic is more harmful and more difficult to remove from water.
How does iron oxide remove arsenic?
Iron oxide adsorption treatment for arsenic in groundwater is a commonly practiced removal process which involves the chemical treatment of arsenic species such that they adsorb onto iron oxides and create larger particles that may be filtered out of the water stream.
What are the sources of arsenic?
Environmental sources of arsenic exposure are. food, water, soil, and. air. Because it is an element, arsenic persists in the environment and does not deteriorate. Arsenic production has greatly decreased in the United States, but imports of arsenic have increased steadily.
Which is the most toxic arsenic?
Arsine gas is the most toxic arsenical (acute exposure).
How many groups of arsenic compounds are there?
Arsenic compounds can be classified into three major groups:
Is arsenic more toxic than organic?
Inorganic arsenic is generally more toxic than organic arsenic. Forms of arsenic that are more rapidly absorbed are more toxic, while those most rapidly eliminated tend to be less toxic. Arsenite and arsenate forms are highly soluble in water.
Is arsenic a toxic substance?
Although organic arsenicals are usually viewed as being less toxic than the in organics , several methyl and phenyl derivatives of arsenic that are widely used in agriculture are of possible health concern on the basis mostly of animal studies. Chief among these are monomethylarsonic acid (MMA) and its salts and dimethylarsinic acid (DMA) and its salts, and roxarsone [ATSDR 2007].
What is activated alumina?
Activated alumina has a long history of use as an adsorptive treatment technology for arsenic removal. The media is a by-product of aluminium production. It is primarily an aluminium oxide that has been activated by exposure to high temperature and caustic soda. The material is extremely porous and has a high average surface area per unit weight (~350 m2/g). The capacity for arsenic removal by activated alumina is pH dependent, with the maximum removal capacity achieved at pH 5.5. Adjusting the pH of the source water, therefore, provides removal capacity advantages. As the pH deviates from the 5.0 – 6.0 range, the adsorption capacity for arsenic decreases at an increasing rate. It has been observed that that arsenic removal capacity has been reduced by more than 15% at pH 6.0 compared to that of pH 5.5.
What is reverse osmosis?
Reverse Osmosis or hyper filtration as it is called due to ability of membranes to filter out the ions. The membranes are not ion selective though and will remove almost all the salts. The salt rejection can be achieved up to 99.5 % in some membranes & hence can be successfully implemented for Arsenic removal also. The only flip side of RO process is the extensive pre-treatment & power required to force the pure water through the membranes.
What is the advantage of ion exchange?
Capable of complete removal of all dissolved matter, including arsenic, from water, this process is widely used for the production of deionized water. One great advantage of Ion Exchange is that no pH adjustment is necessary. Recent advances in resin technology have replaced the weak-base anion resins with strong-base ones. Pentavalent arsenic (As+5), being present as the divalent anion HAsO4
Is arsenic an acid?
Both oxides are acidic, when hydrolyzed they form oxo-acidic compounds. Similar to phosphorus chemistry, trivalent arsenic oxide is hydrolyzed to arsenious acid in the reaction:
Abstract
The performance of a novel combined process, consisting of pre-oxidation, co-precipitation, adsorption and coagulation was investigated for treatment of high arsenic content industrial wastewater. KMnO 4 was used to oxidize As (III) to As (V) firstly, meanwhile the total arsenic concentration reduced about 9%.
1. Introduction
Most environmental arsenic problems were the result of mobilization under natural conditions. However, effluents from industries such as mining, smelting and petroleum processes had high arsenic content [1], [2], [3].
2. Materials and methods
Potassium permanganate (KMnO 4, 99%), calcium hypochlorite (Ca (ClO) 2, 70%), lime (CaO, 90%), hydrated ferrous sulfate (FeSO 4 ·7H 2 O, 95%), and PACl of commercial grade were utilized in the experiments. FMBO was freshly synthesized on-site by combination of the solution of KMnO 4 and FeSO 4 ·7H 2 O stoichiometrically.
3. Results and discussion
In the preliminary experiments, KMnO 4 and Ca (ClO) 2 were used as pre-oxidants to oxide As (III) into As (V). Results showed that KMnO 4 had higher efficiency for As (III) oxidation than that of Ca (ClO) 2. So KMnO 4 was chosen as the pre-oxidant.
4. Conclusions
High arsenic acidic wastewater with average concentration of 465 mg/L was effectively and safe treated and disposed by the combined process of pre-oxidation, lime and ferrous precipitation, FMBO adsorption and PACl flocculation. Pre-oxidation was necessary because of 120–150 mg/L of As (III) in the acidic wastewater.
Acknowledgments
This work was supported by the National High-tech R&D Programme of China (no. 2009AA062905) and the Technology Innovation Programme of Beijing Forestry University of China (no. TD2010-5).
How many minerals are in arsenic?
Arsenic is associated with as many as 120 naturally occurring minerals,mainly sulphides. The common arsenic minerals are listed in Table 1. Mostof them are found to be associated with different transition metals.
What is the atomic mass of arsenic?
Arsenic belongs to p–block in the periodic table. Fig. 1 shows the Bohr’satomic model of arsenic having atomic number 33 and atomic mass 75 amu.It comes under the category of metalloids. It can exist in different allotropes.It is mainly used as a dopant in n–type semiconductor.
Can ferric arsenate be precipiated?
Ferric arsenate can be precipiated by using both ferrous and ferric ions.The role of oxidant is to oxidize As (III) (arsenite) to As (V) (arsenate) andsimultaneously oxidizing ferrous ions to ferric ions which combines toprecipitate ferric arsenate as described in equation (2) to (4) (Sahu et al.).
Can arsenic be precipitated?
Arsenic can be precipitated as ferric arsenate with both ferrous and ferricion. The stability in terms of leachability is both pH and elemental ratiodependent. The present study reveals that the ferric arsenate precipitationis a robust process that withstands temperature drops and even can beadopted in the presence of other elements. Precipitation of ferric arsenateprovides an efficient technique to remove arsenic from the effluents aswell as getting a useful product on the other hand. It is very practical formetallurgical industries dealing with arsenic containing solutions such ascopper refineries, zinc refineries, etc. The arsenic free effluents can berecycled back, if possible which was not permitted earlier. Thus a closedflow circuit can be developed and it would result in re–utilization of severalother elements present in the effluents economically and in eco–friendlyway.