Arsenic removal from water
AssigneeSandia Corporation
InventorsRobert C. Moore, D. Richard Anderson
Life of this patent
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Abstract
Methods for removing arsenic from water by addition of inexpensive and commonly available magnesium oxide, magnesium hydroxide, calcium oxide, or calcium hydroxide to the water. The hydroxide has a strong chemical affinity for arsenic and rapidly adsorbs arsenic, even in the presence of carbonate in the water. Simple and commercially available mechanical methods for removal of magnesium hydroxide particles with adsorbed arsenic from drinking water can be used, including filtration, dissolved air flotation, vortex separation, or centrifugal separation. A method for continuous removal of arsenic from water is provided. Also provided is a method for concentrating arsenic in a water sample to facilitate quantification of arsenic, by means of magnesium or calcium hydroxide adsorption.
Claims58
A continuous process for reducing the concentration of arsenic in water to below an acceptable level and for recycling magnesium, comprising:
- a) adding magnesium hydroxide to the water;
- b) adsorbing arsenic on the magnesium hydroxide;
- c) separating and removing from the water the magnesium hydroxide with adsorbed arsenic, thereby reducing the concentration of arsenic in the water to below the acceptable level;
- d) making an aqueous solution comprising the magnesium hydroxide with adsorbed arsenic removed in step c);
- e) converting the magnesium hydroxide with adsorbed arsenic to magnesium carbonate, whereupon free arsenic is released into the solution;
- f) separating and removing the magnesium carbonate from the solution;
- g) heating the magnesium carbonate to produce carbon dioxide and purified magnesium oxide;
- and
- h) providing the purified magnesium oxide produced in step g) to step a), whereby the magnesium is recycled.
A method of concentrating arsenic from a sample of arsenic contaminated water, comprising:
- a) adding magnesium hydroxide to a first sample of the arsenic contaminated water;
- b) adsorbing arsenic on the magnesium hydroxide;
- c) separating and removing from the first sample the magnesium hydroxide with adsorbed arsenic;
- d) adding the magnesium hydroxide with adsorbed arsenic removed in step c) to a second sample of water, wherein the volume of liquid in the second sample is substantially less than the volume of liquid in the first sample;
- and
- e) converting the magnesium hydroxide with adsorbed arsenic in the second sample to magnesium carbonate, whereupon free arsenic is released into solution, whereby the concentration of free arsenic in the second sample is concentrated relative to the first sample by the ratio of the volume of liquid in the first sample divided by the volume of liquid in the second sample.
A method of concentrating arsenic from a sample of water contaminated with arsenic and at least one other impurity, comprising:
- a) adding magnesium hydroxide to a first sample of the contaminated water;
- b) adsorbing arsenic on the magnesium hydroxide;
- c) separating and removing from the first sample the magnesium hydroxide with adsorbed arsenic;
- d) adding the magnesium hydroxide with adsorbed arsenic removed in step c) to a second sample of water, wherein the volume of liquid in the second sample is substantially less than the volume of liquid in the first sample, and wherein the water in the second sample consists of essentially pure water without arsenic or other impurities;
- and
- e) converting the magnesium hydroxide with adsorbed arsenic in the second sample to magnesium carbonate;
- whereupon free arsenic is released into solution;
- whereby the concentration of free arsenic in the second sample is concentrated relative to the first sample by the ratio of the volume of liquid in the first sample divided by the volume of liquid in the second sample;
- and further wherein the at least one impurity in the first sample is not transferred to the second sample.
Dependencies are inferred from the claim text.